Exemple #1
0
/**
    Purpose
    -------
    SGETRF_m computes an LU factorization of a general M-by-N matrix A
    using partial pivoting with row interchanges.  This version does not
    require work space on the GPU passed as input. GPU memory is allocated
    in the routine. The matrix may exceed the GPU memory.

    The factorization has the form
       A = P * L * U
    where P is a permutation matrix, L is lower triangular with unit
    diagonal elements (lower trapezoidal if m > n), and U is upper
    triangular (upper trapezoidal if m < n).

    This is the right-looking Level 3 BLAS version of the algorithm.

    Note: The factorization of big panel is done calling multiple-gpu-interface.
    Pivots are applied on GPU within the big panel.

    Arguments
    ---------
    @param[in]
    num_gpus INTEGER
             The number of GPUs.  num_gpus > 0.

    @param[in]
    m       INTEGER
            The number of rows of the matrix A.  M >= 0.

    @param[in]
    n       INTEGER
            The number of columns of the matrix A.  N >= 0.

    @param[in,out]
    A       REAL array, dimension (LDA,N)
            On entry, the M-by-N matrix to be factored.
            On exit, the factors L and U from the factorization
            A = P*L*U; the unit diagonal elements of L are not stored.
    \n
            Higher performance is achieved if A is in pinned memory, e.g.
            allocated using magma_malloc_pinned.

    @param[in]
    lda     INTEGER
            The leading dimension of the array A.  LDA >= max(1,M).

    @param[out]
    ipiv    INTEGER array, dimension (min(M,N))
            The pivot indices; for 1 <= i <= min(M,N), row i of the
            matrix was interchanged with row IPIV(i).

    @param[out]
    info    INTEGER
      -     = 0:  successful exit
      -     < 0:  if INFO = -i, the i-th argument had an illegal value
                  or another error occured, such as memory allocation failed.
      -     > 0:  if INFO = i, U(i,i) is exactly zero. The factorization
                  has been completed, but the factor U is exactly
                  singular, and division by zero will occur if it is used
                  to solve a system of equations.

    @ingroup magma_sgesv_comp
    ********************************************************************/
extern "C" magma_int_t
magma_sgetrf_m(magma_int_t num_gpus, magma_int_t m, magma_int_t n,
               float *A, magma_int_t lda,
               magma_int_t *ipiv, magma_int_t *info)
{
#define     A(i,j) (A      + (j)*lda + (i))
#define dAT(d,i,j) (dAT[d] + (i)*nb*ldn_local + (j)*nb)
#define dPT(d,i,j) (dPT[d] + (i)*nb*nb + (j)*nb*maxm)

    magma_timer_t time=0, time_total=0, time_alloc=0, time_set=0, time_get=0, time_comp=0;
    timer_start( time_total );
    real_Double_t flops;

    float c_one     = MAGMA_S_ONE;
    float c_neg_one = MAGMA_S_NEG_ONE;
    float *dAT[MagmaMaxGPUs], *dA[MagmaMaxGPUs], *dPT[MagmaMaxGPUs];
    magma_int_t        iinfo = 0, nb, nbi, maxm, n_local[MagmaMaxGPUs], ldn_local;
    magma_int_t        N, M, NB, NBk, I, d, num_gpus0 = num_gpus;
    magma_int_t        ii, jj, h, offset, ib, rows, s;
    
    magma_queue_t stream[MagmaMaxGPUs][2];
    magma_event_t  event[MagmaMaxGPUs][2];

    *info = 0;
    if (m < 0)
        *info = -1;
    else if (n < 0)
        *info = -2;
    else if (lda < max(1,m))
        *info = -4;

    if (*info != 0) {
        magma_xerbla( __func__, -(*info) );
        return *info;
    }

    /* Quick return if possible */
    if (m == 0 || n == 0)
        return *info;

    magma_device_t orig_dev;
    magma_getdevice( &orig_dev );
    magma_queue_t orig_stream;
    magmablasGetKernelStream( &orig_stream );
    
    /* initialize nb */
    nb = magma_get_sgetrf_nb(m);
    maxm = ((m  + 31)/32)*32;

    /* figure out NB */
    size_t freeMem, totalMem;
    cudaMemGetInfo( &freeMem, &totalMem );
    freeMem /= sizeof(float);
    
    /* number of columns in the big panel */
    h = 1+(2+num_gpus0);
    NB = (magma_int_t)(0.8*freeMem/maxm-h*nb);
    const char* ngr_nb_char = getenv("MAGMA_NGR_NB");
    if ( ngr_nb_char != NULL )
        NB = max( nb, min( NB, atoi(ngr_nb_char) ) );
    //NB = 5*max(nb,32);

    if ( num_gpus0 > ceil((float)NB/nb) ) {
        num_gpus = (int)ceil((float)NB/nb);
        h = 1+(2+num_gpus);
        NB = (magma_int_t)(0.8*freeMem/maxm-h*nb);
    } else {
        num_gpus = num_gpus0;
    }
    if ( num_gpus*NB >= n ) {
        #ifdef CHECK_SGETRF_OOC
        printf( "      * still fit in GPU memory.\n" );
        #endif
        NB = n;
    } else {
        #ifdef CHECK_SGETRF_OOC
        printf( "      * don't fit in GPU memory.\n" );
        #endif
        NB = num_gpus*NB;
        NB = max( nb, (NB / nb) * nb); /* making sure it's devisable by nb (x64) */
    }

    #ifdef CHECK_SGETRF_OOC
    if ( NB != n ) printf( "      * running in out-core mode (n=%d, NB=%d, nb=%d, freeMem=%.2e).\n", n, NB, nb, (float)freeMem );
    else           printf( "      * running in in-core mode  (n=%d, NB=%d, nb=%d, freeMem=%.2e).\n", n, NB, nb, (float)freeMem );
    #endif

    if ( (nb <= 1) || (nb >= min(m,n)) ) {
        /* Use CPU code for scalar of one tile. */
        lapackf77_sgetrf(&m, &n, A, &lda, ipiv, info);
    } else {
        /* Use hybrid blocked code. */

        /* allocate memory on GPU to store the big panel */
        timer_start( time_alloc );
        n_local[0] = (NB/nb)/num_gpus;
        if ( NB%(nb*num_gpus) != 0 )
            n_local[0]++;
        n_local[0] *= nb;
        ldn_local = ((n_local[0]+31)/32)*32;
    
        for( d=0; d < num_gpus; d++ ) {
            magma_setdevice(d);
            if (MAGMA_SUCCESS != magma_smalloc( &dA[d], (ldn_local+h*nb)*maxm )) {
                *info = MAGMA_ERR_DEVICE_ALLOC;
                return *info;
            }
            dPT[d] = dA[d] + nb*maxm;      /* for storing the previous panel from CPU */
            dAT[d] = dA[d] + h*nb*maxm;    /* for storing the big panel               */
            magma_queue_create( &stream[d][0] );
            magma_queue_create( &stream[d][1] );
            magma_event_create( &event[d][0] );
            magma_event_create( &event[d][1] );
        }
        //magma_setdevice(0);
        timer_stop( time_alloc );
        
        for( I=0; I < n; I += NB ) {
            M = m;
            N = min( NB, n-I );       /* number of columns in this big panel             */
            s = min( max(m-I,0), N )/nb; /* number of small block-columns in this big panel */
    
            maxm = ((M + 31)/32)*32;
            if ( num_gpus0 > ceil((float)N/nb) ) {
                num_gpus = (int)ceil((float)N/nb);
            } else {
                num_gpus = num_gpus0;
            }
    
            for( d=0; d < num_gpus; d++ ) {
                n_local[d] = ((N/nb)/num_gpus)*nb;
                if (d < (N/nb)%num_gpus)
                    n_local[d] += nb;
                else if (d == (N/nb)%num_gpus)
                    n_local[d] += N%nb;
            }
            ldn_local = ((n_local[0]+31)/32)*32;
            
            /* upload the next big panel into GPU, transpose (A->A'), and pivot it */
            timer_start( time );
            magmablas_ssetmatrix_transpose_mgpu(num_gpus, stream, A(0,I), lda,
                                                dAT, ldn_local, dA, maxm, M, N, nb);
            for( d=0; d < num_gpus; d++ ) {
                magma_setdevice(d);
                magma_queue_sync( stream[d][0] );
                magma_queue_sync( stream[d][1] );
            magmablasSetKernelStream(NULL);
            }
            time_set += timer_stop( time );
    
            timer_start( time );
            /* == --------------------------------------------------------------- == */
            /* == loop around the previous big-panels to update the new big-panel == */
            for( offset = 0; offset < min(m,I); offset += NB ) {
                NBk = min( m-offset, NB );
                /* start sending the first tile from the previous big-panels to gpus */
                for( d=0; d < num_gpus; d++ ) {
                    magma_setdevice(d);
                    nbi  = min( nb, NBk );
                    magma_ssetmatrix_async( (M-offset), nbi,
                                            A(offset,offset), lda,
                                            dA[d],            (maxm-offset), stream[d][0] );
                    
                    /* make sure the previous update finished */
                    magmablasSetKernelStream(stream[d][0]);
                    //magma_queue_sync( stream[d][1] );
                    magma_queue_wait_event( stream[d][0], event[d][0] );
                    
                    /* transpose */
                    magmablas_stranspose( M-offset, nbi, dA[d], maxm-offset, dPT(d,0,0), nb );
                }
                
                /* applying the pivot from the previous big-panel */
                for( d=0; d < num_gpus; d++ ) {
                    magma_setdevice(d);
                    magmablasSetKernelStream(stream[d][1]);
                    magmablas_spermute_long3( dAT(d,0,0), ldn_local, ipiv, NBk, offset );
                }
                
                /* == going through each block-column of previous big-panels == */
                for( jj=0, ib=offset/nb; jj < NBk; jj += nb, ib++ ) {
                    ii   = offset+jj;
                    rows = maxm - ii;
                    nbi  = min( nb, NBk-jj );
                    for( d=0; d < num_gpus; d++ ) {
                        magma_setdevice(d);
                        
                        /* wait for a block-column on GPU */
                        magma_queue_sync( stream[d][0] );
                        
                        /* start sending next column */
                        if ( jj+nb < NBk ) {
                            magma_ssetmatrix_async( (M-ii-nb), min(nb,NBk-jj-nb),
                                                    A(ii+nb,ii+nb), lda,
                                                    dA[d],          (rows-nb), stream[d][0] );
                            
                            /* make sure the previous update finished */
                            magmablasSetKernelStream(stream[d][0]);
                            //magma_queue_sync( stream[d][1] );
                            magma_queue_wait_event( stream[d][0], event[d][(1+jj/nb)%2] );
                            
                            /* transpose next column */
                            magmablas_stranspose( M-ii-nb, nb, dA[d], rows-nb, dPT(d,0,(1+jj/nb)%2), nb );
                        }
                        
                        /* update with the block column */
                        magmablasSetKernelStream(stream[d][1]);
                        magma_strsm( MagmaRight, MagmaUpper, MagmaNoTrans, MagmaUnit,
                                     n_local[d], nbi, c_one, dPT(d,0,(jj/nb)%2), nb, dAT(d,ib,0), ldn_local );
                        if ( M > ii+nb ) {
                            magma_sgemm( MagmaNoTrans, MagmaNoTrans,
                                n_local[d], M-(ii+nb), nbi, c_neg_one, dAT(d,ib,0), ldn_local,
                                dPT(d,1,(jj/nb)%2), nb, c_one, dAT(d,ib+1,0), ldn_local );
                        }
                        magma_event_record( event[d][(jj/nb)%2], stream[d][1] );
                    
                    } /* end of for each block-columns in a big-panel */
                }
            } /* end of for each previous big-panels */
            for( d=0; d < num_gpus; d++ ) {
                magma_setdevice(d);
                magma_queue_sync( stream[d][0] );
                magma_queue_sync( stream[d][1] );
            magmablasSetKernelStream(NULL);
            }
    
            /* calling magma-gpu interface to panel-factorize the big panel */
            if ( M > I ) {
                //magma_sgetrf1_mgpu(num_gpus, M-I, N, nb, I, dAT, ldn_local, ipiv+I, dA, A(0,I), lda,
                //                   (magma_queue_t **)stream, &iinfo);
                magma_sgetrf2_mgpu(num_gpus, M-I, N, nb, I, dAT, ldn_local, ipiv+I, dA, A(0,I), lda,
                                   stream, &iinfo);
                if ( iinfo < 0 ) {
                    *info = iinfo;
                    break;
                } else if ( iinfo != 0 ) {
                    *info = iinfo + I * NB;
                    //break;
                }
                /* adjust pivots */
                for( ii=I; ii < min(I+N,m); ii++ )
                    ipiv[ii] += I;
            }
            time_comp += timer_stop( time );
    
            /* download the current big panel to CPU */
            timer_start( time );
            magmablas_sgetmatrix_transpose_mgpu(num_gpus, stream, dAT, ldn_local, A(0,I), lda, dA, maxm, M, N, nb);
            for( d=0; d < num_gpus; d++ ) {
                magma_setdevice(d);
                magma_queue_sync( stream[d][0] );
                magma_queue_sync( stream[d][1] );
            magmablasSetKernelStream(NULL);
            }
            time_get += timer_stop( time );
        } /* end of for */
    
        timer_stop( time_total );
        flops = FLOPS_SGETRF( m, n ) / 1e9;
        timer_printf(" memory-allocation time: %e\n", time_alloc );
        timer_printf(" NB=%d nb=%d\n", (int) NB, (int) nb );
        timer_printf(" memcopy and transpose %e seconds\n", time_set );
        timer_printf(" total time %e seconds\n", time_total );
        timer_printf(" Performance %f GFlop/s, %f seconds without htod and dtoh\n",     flops / (time_comp),               time_comp               );
        timer_printf(" Performance %f GFlop/s, %f seconds with    htod\n",              flops / (time_comp + time_set),    time_comp + time_set    );
        timer_printf(" Performance %f GFlop/s, %f seconds with    dtoh\n",              flops / (time_comp + time_get),    time_comp + time_get    );
        timer_printf(" Performance %f GFlop/s, %f seconds without memory-allocation\n", flops / (time_total - time_alloc), time_total - time_alloc );
    
        for( d=0; d < num_gpus0; d++ ) {
            magma_setdevice(d);
            magma_free( dA[d] );
            magma_event_destroy( event[d][0] );
            magma_event_destroy( event[d][1] );
            magma_queue_destroy( stream[d][0] );
            magma_queue_destroy( stream[d][1] );
        }
        magma_setdevice( orig_dev );
        magmablasSetKernelStream( orig_stream );
    }
    if ( *info >= 0 )
        magma_sgetrf_piv(m, n, NB, A, lda, ipiv, info);
    return *info;
} /* magma_sgetrf_m */
Exemple #2
0
/**
    Purpose
    -------
    SGETRF computes an LU factorization of a general M-by-N matrix A
    using partial pivoting with row interchanges.

    The factorization has the form
       A = P * L * U
    where P is a permutation matrix, L is lower triangular with unit
    diagonal elements (lower trapezoidal if m > n), and U is upper
    triangular (upper trapezoidal if m < n).

    This is the right-looking Level 3 BLAS version of the algorithm.
    Use two buffer to send panels.

    Arguments
    ---------
    @param[in]
    num_gpus INTEGER
            The number of GPUs to be used for the factorization.

    @param[in]
    m       INTEGER
            The number of rows of the matrix A.  M >= 0.

    @param[in]
    n       INTEGER
            The number of columns of the matrix A.  N >= 0.

    @param[in,out]
    A       REAL array on the GPU, dimension (LDDA,N).
            On entry, the M-by-N matrix to be factored.
            On exit, the factors L and U from the factorization
            A = P*L*U; the unit diagonal elements of L are not stored.

    @param[in]
    ldda    INTEGER
            The leading dimension of the array A.  LDDA >= max(1,M).

    @param[out]
    ipiv    INTEGER array, dimension (min(M,N))
            The pivot indices; for 1 <= i <= min(M,N), row i of the
            matrix was interchanged with row IPIV(i).

    @param[out]
    info    INTEGER
      -     = 0:  successful exit
      -     < 0:  if INFO = -i, the i-th argument had an illegal value
                  or another error occured, such as memory allocation failed.
      -     > 0:  if INFO = i, U(i,i) is exactly zero. The factorization
                  has been completed, but the factor U is exactly
                  singular, and division by zero will occur if it is used
                  to solve a system of equations.

    @ingroup magma_sgesv_comp
    ********************************************************************/
extern "C" magma_int_t
magma_sgetrf2_mgpu(magma_int_t num_gpus,
         magma_int_t m, magma_int_t n, magma_int_t nb, magma_int_t offset,
         float *d_lAT[], magma_int_t lddat, magma_int_t *ipiv,
         float *d_lAP[], float *w, magma_int_t ldw,
         magma_queue_t streaml[][2], magma_int_t *info)
{
#define dAT(id,i,j)  (d_lAT[(id)] + ((offset)+(i)*nb)*lddat + (j)*nb)
#define W(j) (w+((j)%num_gpus)*nb*ldw)

    float c_one     = MAGMA_S_ONE;
    float c_neg_one = MAGMA_S_NEG_ONE;

    magma_int_t block_size = 32;
    magma_int_t iinfo, n_local[MagmaMaxGPUs];
    magma_int_t maxm, mindim;
    magma_int_t i, d, dd, rows, cols, s, ldpan[MagmaMaxGPUs];
    magma_int_t id, i_local, i_local2, nb0, nb1, h = 2+num_gpus;
    float *d_panel[MagmaMaxGPUs], *panel_local[MagmaMaxGPUs];

    /* Check arguments */
    *info = 0;
    if (m < 0)
        *info = -2;
    else if (n < 0)
        *info = -3;
    else if (num_gpus*lddat < max(1,n))
        *info = -5;

    if (*info != 0) {
        magma_xerbla( __func__, -(*info) );
        return *info;
    }

    /* Quick return if possible */
    if (m == 0 || n == 0)
        return *info;

    /* Function Body */
    mindim = min(m, n);
    if ( num_gpus > ceil((float)n/nb) ) {
        *info = -1;
        return *info;
    }

    /* Use hybrid blocked code. */
    maxm  = ((m + block_size-1)/block_size)*block_size;

    /* some initializations */
    for (i=0; i < num_gpus; i++) {
        magma_setdevice(i);
        
        n_local[i] = ((n/nb)/num_gpus)*nb;
        if (i < (n/nb)%num_gpus)
            n_local[i] += nb;
        else if (i == (n/nb)%num_gpus)
            n_local[i] += n%nb;
        
        /* workspaces */
        d_panel[i] = &(d_lAP[i][h*nb*maxm]);   /* temporary panel storage */
    }
    trace_init( 1, num_gpus, 2, (CUstream_st**)streaml );

    /* start sending the panel to cpu */
    nb0 = min(mindim, nb);
    magma_setdevice(0);
    magmablasSetKernelStream(streaml[0][1]);
    trace_gpu_start( 0, 1, "comm", "get" );
    magmablas_stranspose( nb0, m, dAT(0,0,0), lddat, d_lAP[0], maxm );
    magma_sgetmatrix_async( m, nb0,
                            d_lAP[0], maxm,
                            W(0),     ldw, streaml[0][1] );
    trace_gpu_end( 0, 1 );

    /* ------------------------------------------------------------------------------------- */
    magma_timer_t time=0;
    timer_start( time );

    s = mindim / nb;
    for( i=0; i < s; i++ ) {
        /* Set the GPU number that holds the current panel */
        id = i%num_gpus;
        magma_setdevice(id);
        
        /* Set the local index where the current panel is */
        i_local = i/num_gpus;
        cols  = maxm - i*nb;
        rows  = m - i*nb;
        
        /* synchrnoize i-th panel from id-th gpu into work */
        magma_queue_sync( streaml[id][1] );
        
        /* i-th panel factorization */
        trace_cpu_start( 0, "getrf", "getrf" );
        lapackf77_sgetrf( &rows, &nb, W(i), &ldw, ipiv+i*nb, &iinfo);
        if ( (*info == 0) && (iinfo > 0) ) {
            *info = iinfo + i*nb;
        }
        trace_cpu_end( 0 );
        
        /* start sending the panel to all the gpus */
        d = (i+1)%num_gpus;
        for( dd=0; dd < num_gpus; dd++ ) {
            magma_setdevice(d);
            trace_gpu_start( 0, 1, "comm", "set" );
            magma_ssetmatrix_async( rows, nb,
                                    W(i),     ldw,
                                    &d_lAP[d][(i%h)*nb*maxm], cols,
                                    streaml[d][1] );
            trace_gpu_end( 0, 1 );
            d = (d+1)%num_gpus;
        }
        
        /* apply the pivoting */
        d = (i+1)%num_gpus;
        for( dd=0; dd < num_gpus; dd++ ) {
            magma_setdevice(d);
            magmablasSetKernelStream(streaml[d][0]);
            
            trace_gpu_start( d, 1, "pivot", "pivot" );
            if ( dd == 0 )
                magmablas_spermute_long2( lddat, dAT(d,0,0), lddat, ipiv, nb, i*nb );
            else
                magmablas_spermute_long3(        dAT(d,0,0), lddat, ipiv, nb, i*nb );
            trace_gpu_end( d, 1 );
            d = (d+1)%num_gpus;
        }
    
    
        /* update the trailing-matrix/look-ahead */
        d = (i+1)%num_gpus;
        for( dd=0; dd < num_gpus; dd++ ) {
            magma_setdevice(d);
            
            /* storage for panel */
            if ( d == id ) {
                /* the panel belond to this gpu */
                panel_local[d] = dAT(d,i,i_local);
                ldpan[d] = lddat;
                /* next column */
                i_local2 = i_local+1;
            } else {
                /* the panel belong to another gpu */
                panel_local[d] = d_panel[d];
                ldpan[d] = nb;
                /* next column */
                i_local2 = i_local;
                if ( d < id ) i_local2 ++;
            }
            /* the size of the next column */
            if ( s > (i+1) ) {
                nb0 = nb;
            } else {
                nb0 = n_local[d]-nb*(s/num_gpus);
                if ( d < s%num_gpus ) nb0 -= nb;
            }
            if ( d == (i+1)%num_gpus) {
                /* owns the next column, look-ahead the column */
                nb1 = nb0;
                magmablasSetKernelStream(streaml[d][1]);
                
                /* make sure all the pivoting has been applied */
                magma_queue_sync(streaml[d][0]);
                trace_gpu_start( d, 1, "gemm", "gemm" );
                /* transpose panel on GPU */
                magmablas_stranspose( rows, nb, &d_lAP[d][(i%h)*nb*maxm], cols, panel_local[d], ldpan[d] );
                /* synch for remaining update */
                magma_queue_sync(streaml[d][1]);
            } else {
                /* update the entire trailing matrix */
                nb1 = n_local[d] - i_local2*nb;
                magmablasSetKernelStream(streaml[d][0]);
                
                /* synchronization to make sure panel arrived on gpu */
                magma_queue_sync(streaml[d][1]);
                trace_gpu_start( d, 0, "gemm", "gemm" );
                /* transpose panel on GPU */
                magmablas_stranspose( rows, nb, &d_lAP[d][(i%h)*nb*maxm], cols, panel_local[d], ldpan[d] );
            }
            
            /* gpu updating the trailing matrix */
            magma_strsm( MagmaRight, MagmaUpper, MagmaNoTrans, MagmaUnit,
                         nb1, nb, c_one,
                         panel_local[d],       ldpan[d],
                         dAT(d, i, i_local2), lddat);
            magma_sgemm( MagmaNoTrans, MagmaNoTrans,
                         nb1, m-(i+1)*nb, nb,
                         c_neg_one, dAT(d, i,   i_local2),         lddat,
                                    &(panel_local[d][nb*ldpan[d]]), ldpan[d],
                         c_one,     dAT(d, i+1, i_local2),         lddat );
        
            if ( d == (i+1)%num_gpus ) {
                /* Set the local index where the current panel is */
                int loff    = i+1;
                int i_local = (i+1)/num_gpus;
                int ldda    = maxm - (i+1)*nb;
                int cols    = m - (i+1)*nb;
                nb0 = min(nb, mindim - (i+1)*nb); /* size of the diagonal block */
                trace_gpu_end( d, 1 );
                
                if ( nb0 > 0 ) {
                    /* transpose the panel for sending it to cpu */
                    trace_gpu_start( d, 1, "comm", "get" );
                    magmablas_stranspose( nb0, m-(i+1)*nb, dAT(d,loff,i_local), lddat, &d_lAP[d][((i+1)%h)*nb*maxm], ldda );
             
                    /* send the panel to cpu */
                    magma_sgetmatrix_async( cols, nb0,
                                            &d_lAP[d][((i+1)%h)*nb*maxm], ldda,
                                            W(i+1), ldw, streaml[d][1] );

                    trace_gpu_end( d, 1 );
                }
            } else {
                trace_gpu_end( d, 0 );
            }
            
            d = (d+1)%num_gpus;
        }
    
        /* update the remaining matrix by gpu owning the next panel */
        if ( (i+1) < s ) {
            int i_local = (i+1)/num_gpus;
            int rows  = m - (i+1)*nb;
            
            d = (i+1)%num_gpus;
            magma_setdevice(d);
            magmablasSetKernelStream(streaml[d][0]);
            trace_gpu_start( d, 0, "gemm", "gemm" );

            magma_strsm( MagmaRight, MagmaUpper, MagmaNoTrans, MagmaUnit,
                         n_local[d] - (i_local+1)*nb, nb,
                         c_one, panel_local[d],       ldpan[d],
                                dAT(d,i,i_local+1),  lddat );
            magma_sgemm( MagmaNoTrans, MagmaNoTrans,
                         n_local[d]-(i_local+1)*nb, rows, nb,
                         c_neg_one, dAT(d,i,i_local+1),            lddat,
                                    &(panel_local[d][nb*ldpan[d]]), ldpan[d],
                         c_one,     dAT(d,i+1,  i_local+1),        lddat );
            trace_gpu_end( d, 0 );
        }
    } /* end of for i=1..s */
    /* ------------------------------------------------------------------------------ */
    
    /* Set the GPU number that holds the last panel */
    id = s%num_gpus;
    
    /* Set the local index where the last panel is */
    i_local = s/num_gpus;
    
    /* size of the last diagonal-block */
    nb0 = min(m - s*nb, n - s*nb);
    rows = m    - s*nb;
    cols = maxm - s*nb;
    
    if ( nb0 > 0 ) {
        magma_setdevice(id);
        
        /* wait for the last panel on cpu */
        magma_queue_sync( streaml[id][1] );
    
        /* factor on cpu */
        lapackf77_sgetrf( &rows, &nb0, W(s), &ldw, ipiv+s*nb, &iinfo);
        if ( (*info == 0) && (iinfo > 0) )
            *info = iinfo + s*nb;
        
        /* send the factor to gpus */
        for( d=0; d < num_gpus; d++ ) {
            magma_setdevice(d);
            i_local2 = i_local;
            if ( d < id ) i_local2 ++;
            
            if ( d == id || n_local[d] > i_local2*nb ) {
                magma_ssetmatrix_async( rows, nb0,
                                        W(s),     ldw,
                                        &d_lAP[d][(s%h)*nb*maxm],
                                        cols, streaml[d][1] );
            }
        }
        
        for( d=0; d < num_gpus; d++ ) {
            magma_setdevice(d);
            magmablasSetKernelStream(streaml[d][0]);
            if ( d == 0 )
                magmablas_spermute_long2( lddat, dAT(d,0,0), lddat, ipiv, nb0, s*nb );
            else
                magmablas_spermute_long3(        dAT(d,0,0), lddat, ipiv, nb0, s*nb );
        }
        
        for( d=0; d < num_gpus; d++ ) {
            magma_setdevice(d);
            magmablasSetKernelStream(streaml[d][1]);
            
            /* wait for the pivoting to be done */
            magma_queue_sync( streaml[d][0] );
            
            i_local2 = i_local;
            if ( d < id ) i_local2++;
            if ( d == id ) {
                /* the panel belond to this gpu */
                panel_local[d] = dAT(d,s,i_local);
                
                /* next column */
                nb1 = n_local[d] - i_local*nb-nb0;
                
                magmablas_stranspose( rows, nb0, &d_lAP[d][(s%h)*nb*maxm], cols, panel_local[d], lddat );
                
                if ( nb1 > 0 ) {
                    magma_strsm( MagmaRight, MagmaUpper, MagmaNoTrans, MagmaUnit,
                                 nb1, nb0, c_one,
                                 panel_local[d],        lddat,
                                 dAT(d,s,i_local)+nb0, lddat);
                }
            } else if ( n_local[d] > i_local2*nb ) {
                /* the panel belong to another gpu */
                panel_local[d] = d_panel[d];
                
                /* next column */
                nb1 = n_local[d] - i_local2*nb;
                
                magmablas_stranspose( rows, nb0, &d_lAP[d][(s%h)*nb*maxm], cols, panel_local[d], nb );
                magma_strsm( MagmaRight, MagmaUpper, MagmaNoTrans, MagmaUnit,
                             nb1, nb0, c_one,
                             panel_local[d],     nb,
                             dAT(d,s,i_local2), lddat);
            }
        }
    } /* if ( nb0 > 0 ) */
    
    /* clean up */
    trace_finalize( "sgetrf_mgpu.svg","trace.css" );
    for( d=0; d < num_gpus; d++ ) {
        magma_setdevice(d);
        magma_queue_sync( streaml[d][0] );
        magma_queue_sync( streaml[d][1] );
        magmablasSetKernelStream(NULL);
    }
    magma_setdevice(0);
    
    timer_start( time );
    timer_printf("\n Performance %f GFlop/s\n", FLOPS_SGETRF(m,n) / 1e9 / time );

    return *info;
} /* magma_sgetrf2_mgpu */