From: "Bryan O'Sullivan" In cases where a large incoming RDMA is being received, we have to copy data inside the interrupt handler before we can ACK each packet. The source is DMAed to by the hardware, which means that the CPU won't have it cached. We only read the source this one time; using normal load instructions pollutes the dcache with useless data, reducing performance to the point where we can lose a significant number of packets. We use memcpy_uncached_read to try to not fill the dcache with useless data. Avoiding the cache refill penalty lets us keep up better with the sender, resulting in many fewer dropped packets. Signed-off-by: Bryan O'Sullivan Cc: Andi Kleen Cc: Roland Dreier Signed-off-by: Andrew Morton --- drivers/infiniband/hw/ipath/ipath_verbs.c | 2 +- 1 files changed, 1 insertion(+), 1 deletion(-) diff -puN drivers/infiniband/hw/ipath/ipath_verbs.c~ib-ipath-use-memcpy_uncached_read-in-rdma-interrupt drivers/infiniband/hw/ipath/ipath_verbs.c --- a/drivers/infiniband/hw/ipath/ipath_verbs.c~ib-ipath-use-memcpy_uncached_read-in-rdma-interrupt +++ a/drivers/infiniband/hw/ipath/ipath_verbs.c @@ -167,7 +167,7 @@ void ipath_copy_sge(struct ipath_sge_sta BUG_ON(len == 0); if (len > length) len = length; - memcpy(sge->vaddr, data, len); + memcpy_uncached_read(sge->vaddr, data, len); sge->vaddr += len; sge->length -= len; sge->sge_length -= len; _