From 911965ace9386e35ca022a65bb45a32fd421af3e Mon Sep 17 00:00:00 2001 From: Li Zhijian Date: Fri, 10 Sep 2021 15:02:55 +0800 Subject: [PATCH] migration/rdma: advise prefetch write for ODP region 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 Reviewed-by: Marcel Apfelbaum Reviewed-by: Juan Quintela Signed-off-by: Juan Quintela --- meson.build | 6 ++++++ migration/rdma.c | 42 ++++++++++++++++++++++++++++++++++++++++++ migration/trace-events | 1 + 3 files changed, 49 insertions(+) diff --git a/meson.build b/meson.build index 5e7946776d..9ed9a993e2 100644 --- a/meson.build +++ b/meson.build @@ -1530,6 +1530,12 @@ config_host_data.set('HAVE_COPY_FILE_RANGE', cc.has_function('copy_file_range')) config_host_data.set('HAVE_OPENPTY', cc.has_function('openpty', dependencies: util)) config_host_data.set('HAVE_STRCHRNUL', cc.has_function('strchrnul')) config_host_data.set('HAVE_SYSTEM_FUNCTION', cc.has_function('system', prefix: '#include ')) +if rdma.found() + config_host_data.set('HAVE_IBV_ADVISE_MR', + cc.has_function('ibv_advise_mr', + args: config_host['RDMA_LIBS'].split(), + prefix: '#include ')) +endif # has_header_symbol config_host_data.set('CONFIG_BYTESWAP_H', diff --git a/migration/rdma.c b/migration/rdma.c index eb80431aae..2a3c7889b9 100644 --- a/migration/rdma.c +++ b/migration/rdma.c @@ -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]) { diff --git a/migration/trace-events b/migration/trace-events index 5f6aa580de..a8ae163707 100644 --- a/migration/trace-events +++ b/migration/trace-events @@ -213,6 +213,7 @@ qemu_rdma_poll_other(const char *compstr, int64_t comp, int left) "other complet qemu_rdma_post_send_control(const char *desc) "CONTROL: sending %s.." qemu_rdma_register_and_get_keys(uint64_t len, void *start) "Registering %" PRIu64 " bytes @ %p" qemu_rdma_register_odp_mr(const char *name) "Try to register On-Demand Paging memory region: %s" +qemu_rdma_advise_mr(const char *name, uint32_t len, uint64_t addr, const char *res) "Try to advise block %s prefetch at %" PRIu32 "@0x%" PRIx64 ": %s" qemu_rdma_registration_handle_compress(int64_t length, int index, int64_t offset) "Zapping zero chunk: %" PRId64 " bytes, index %d, offset %" PRId64 qemu_rdma_registration_handle_finished(void) "" qemu_rdma_registration_handle_ram_blocks(void) ""