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migration/rdma: advise prefetch write for ODP region

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The responder mr registering with ODP will sent RNR NAK back to
the requester in the face of the page fault.
---------
ibv_poll_cq wc.status=13 RNR retry counter exceeded!
ibv_poll_cq wrid=WRITE RDMA!
---------
ibv_advise_mr(3) helps to make pages present before the actual IO is
conducted so that the responder does page fault as little as possible.

Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Reviewed-by: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Li Zhijian
2021-09-10 15:02:55 +08:00
committed by Juan Quintela
parent e2daccb0d0
commit 911965ace9
3 changed files with 49 additions and 0 deletions
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42
migration/rdma.c
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@@ -1133,6 +1133,32 @@ static bool rdma_support_odp(struct ibv_context *dev)
return false;
}
/*
* ibv_advise_mr to avoid RNR NAK error as far as possible.
* The responder mr registering with ODP will sent RNR NAK back to
* the requester in the face of the page fault.
*/
static void qemu_rdma_advise_prefetch_mr(struct ibv_pd *pd, uint64_t addr,
uint32_t len, uint32_t lkey,
const char *name, bool wr)
{
#ifdef HAVE_IBV_ADVISE_MR
int ret;
int advice = wr ? IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE :
IBV_ADVISE_MR_ADVICE_PREFETCH;
struct ibv_sge sg_list = {.lkey = lkey, .addr = addr, .length = len};
ret = ibv_advise_mr(pd, advice,
IBV_ADVISE_MR_FLAG_FLUSH, &sg_list, 1);
/* ignore the error */
if (ret) {
trace_qemu_rdma_advise_mr(name, len, addr, strerror(errno));
} else {
trace_qemu_rdma_advise_mr(name, len, addr, "successed");
}
#endif
}
static int qemu_rdma_reg_whole_ram_blocks(RDMAContext *rdma)
{
int i;
@@ -1156,6 +1182,15 @@ static int qemu_rdma_reg_whole_ram_blocks(RDMAContext *rdma)
local->block[i].local_host_addr,
local->block[i].length, access);
trace_qemu_rdma_register_odp_mr(local->block[i].block_name);
if (local->block[i].mr) {
qemu_rdma_advise_prefetch_mr(rdma->pd,
(uintptr_t)local->block[i].local_host_addr,
local->block[i].length,
local->block[i].mr->lkey,
local->block[i].block_name,
true);
}
}
if (!local->block[i].mr) {
@@ -1255,6 +1290,13 @@ static int qemu_rdma_register_and_get_keys(RDMAContext *rdma,
/* register ODP mr */
block->pmr[chunk] = ibv_reg_mr(rdma->pd, chunk_start, len, access);
trace_qemu_rdma_register_odp_mr(block->block_name);
if (block->pmr[chunk]) {
qemu_rdma_advise_prefetch_mr(rdma->pd, (uintptr_t)chunk_start,
len, block->pmr[chunk]->lkey,
block->block_name, rkey);
}
}
}
if (!block->pmr[chunk]) {