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    SubjectRe: [PATCH] dmaengine: xgene-dma: Disable memcpy operation due to performance drop
    Date
    On Thursday 08 October 2015 13:55:16 Rameshwar Prasad Sahu wrote:
    > The DMA engine supports memory copy, RAID5 XOR, RAID6 PQ, and other
    > computations. But the bandwidth of the entire DMA engine is shared
    > among all channels. This patch re-configures operations availability
    > such that one can achieve maximum performance for XOR and PQ
    > computation by removing the memory offload operations.
    >
    > Signed-off-by: Rameshwar Prasad Sahu <rsahu@apm.com>
    > ---
    > drivers/dma/xgene-dma.c | 3 +++
    > 1 file changed, 3 insertions(+)
    >
    > diff --git a/drivers/dma/xgene-dma.c b/drivers/dma/xgene-dma.c
    > index 8d57b1b..2998fcb 100644
    > --- a/drivers/dma/xgene-dma.c
    > +++ b/drivers/dma/xgene-dma.c
    > @@ -154,6 +154,7 @@
    > #define XGENE_DMA_MAX_XOR_SRC 5
    > #define XGENE_DMA_16K_BUFFER_LEN_CODE 0x0
    > #define XGENE_DMA_INVALID_LEN_CODE 0x7800000000000000ULL
    > +#undef XGENE_DMA_MEMCPY_ENABLE
    >
    > /* X-Gene DMA descriptor error codes */
    > #define ERR_DESC_AXI 0x01
    > @@ -1707,7 +1708,9 @@ static void xgene_dma_set_caps(struct xgene_dma_chan *chan,
    > dma_cap_zero(dma_dev->cap_mask);
    >
    > /* Set DMA device capability */
    > +#ifdef XGENE_DMA_MEMCPY_ENABLE
    > dma_cap_set(DMA_MEMCPY, dma_dev->cap_mask);
    > +#endif
    > dma_cap_set(DMA_SG, dma_dev->cap_mask);
    >
    > /* Basically here, the X-Gene SoC DMA engine channel 0 supports XOR

    I don't see what the #ifdef gains you here when the setting is
    hardcoded. Why not just remove that DMA_MEMCPY capability completely
    if you don't want to use it?

    Arnd


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