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
---
V3: Fix FreeBSD compiling errors
V2: use IBV_ADVISE_MR_FLAG_FLUSH instead of IB_UVERBS_ADVISE_MR_FLAG_FLUSH
and add Reviewed-by tag. # Marcel
---
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 6e4d2d80343..97406d1b79b 100644
--- a/meson.build
+++ b/meson.build
@@ -1328,6 +1328,12 @@ 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 eb80431aae2..2a3c7889b9f 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 5f6aa580def..a8ae163707c 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
