Re: [PATCH 2/2] migration/rdma: advise prefetch write for ODP region
Hi Marcel
On 22/08/2021 16:39, Marcel Apfelbaum wrote:
> Hi,
>
> On Sat, Jul 31, 2021 at 5:03 PM Li Zhijian wrote:
>> 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
>> ---
>> migration/rdma.c | 40
>> migration/trace-events | 1 +
>> 2 files changed, 41 insertions(+)
>>
>> diff --git a/migration/rdma.c b/migration/rdma.c
>> index 8784b5f22a6..a2ad00d665f 100644
>> --- a/migration/rdma.c
>> +++ b/migration/rdma.c
>> @@ -1117,6 +1117,30 @@ static int qemu_rdma_alloc_qp(RDMAContext *rdma)
>> return 0;
>> }
>>
>> +/*
>> + * 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_write_mr(struct ibv_pd *pd, uint64_t
>> addr,
>> + uint32_t len, uint32_t lkey,
>> + const char *name, bool wr)
>> +{
>> +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,
>> +IB_UVERBS_ADVISE_MR_FLAG_FLUSH, _list, 1);
>> +/* ignore the error */
> Following
> https://github.com/linux-rdma/rdma-core/blob/master/libibverbs/man/ibv_advise_mr.3.md
> it looks like it is a best-effort optimization,
> I don't see any down-sides to it.
> However it seems like it is recommended to use
> IBV_ADVISE_MR_FLAG_FLUSH in order to
> increase the optimization chances.
Good catch, i will update it soon.
Thanks
>
> Anyway
>
> Reviewed-by: Marcel Apfelbaum
>
> Thanks,
> Marcel
>
>
Re: [PATCH 2/2] migration/rdma: advise prefetch write for ODP region
Hi,
On Sat, Jul 31, 2021 at 5:03 PM Li Zhijian wrote:
>
> 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
> ---
> migration/rdma.c | 40
> migration/trace-events | 1 +
> 2 files changed, 41 insertions(+)
>
> diff --git a/migration/rdma.c b/migration/rdma.c
> index 8784b5f22a6..a2ad00d665f 100644
> --- a/migration/rdma.c
> +++ b/migration/rdma.c
> @@ -1117,6 +1117,30 @@ static int qemu_rdma_alloc_qp(RDMAContext *rdma)
> return 0;
> }
>
> +/*
> + * 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_write_mr(struct ibv_pd *pd, uint64_t
> addr,
> + uint32_t len, uint32_t lkey,
> + const char *name, bool wr)
> +{
> +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,
> +IB_UVERBS_ADVISE_MR_FLAG_FLUSH, _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");
> +}
> +}
> +
> static int qemu_rdma_reg_whole_ram_blocks(RDMAContext *rdma)
> {
> int i;
> @@ -1140,6 +1164,17 @@ on_demand:
> perror("Failed to register local dest ram block!\n");
> break;
> }
> +
> +if (access & IBV_ACCESS_ON_DEMAND) {
> +qemu_rdma_advise_prefetch_write_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);
> +}
> +
> rdma->total_registrations++;
> }
>
> @@ -1244,6 +1279,11 @@ on_demand:
> rdma->total_registrations);
> return -1;
> }
> +if (access & IBV_ACCESS_ON_DEMAND) {
> +qemu_rdma_advise_prefetch_write_mr(rdma->pd,
> (uintptr_t)chunk_start,
> + len, block->pmr[chunk]->lkey,
> + block->block_name, rkey);
> +}
> rdma->total_registrations++;
> }
>
> diff --git a/migration/trace-events b/migration/trace-events
> index 5f6aa580def..901c1d54c12 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 write 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) ""
> --
> 2.31.1
>
Following
https://github.com/linux-rdma/rdma-core/blob/master/libibverbs/man/ibv_advise_mr.3.md
it looks like it is a best-effort optimization,
I don't see any down-sides to it.
However it seems like it is recommended to use
IBV_ADVISE_MR_FLAG_FLUSH in order to
increase the optimization chances.
Anyway
Reviewed-by: Marcel Apfelbaum
Thanks,
Marcel
[PATCH 2/2] 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
---
migration/rdma.c | 40
migration/trace-events | 1 +
2 files changed, 41 insertions(+)
diff --git a/migration/rdma.c b/migration/rdma.c
index 8784b5f22a6..a2ad00d665f 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -1117,6 +1117,30 @@ static int qemu_rdma_alloc_qp(RDMAContext *rdma)
return 0;
}
+/*
+ * 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_write_mr(struct ibv_pd *pd, uint64_t
addr,
+ uint32_t len, uint32_t lkey,
+ const char *name, bool wr)
+{
+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,
+IB_UVERBS_ADVISE_MR_FLAG_FLUSH, _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");
+}
+}
+
static int qemu_rdma_reg_whole_ram_blocks(RDMAContext *rdma)
{
int i;
@@ -1140,6 +1164,17 @@ on_demand:
perror("Failed to register local dest ram block!\n");
break;
}
+
+if (access & IBV_ACCESS_ON_DEMAND) {
+qemu_rdma_advise_prefetch_write_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);
+}
+
rdma->total_registrations++;
}
@@ -1244,6 +1279,11 @@ on_demand:
rdma->total_registrations);
return -1;
}
+if (access & IBV_ACCESS_ON_DEMAND) {
+qemu_rdma_advise_prefetch_write_mr(rdma->pd,
(uintptr_t)chunk_start,
+ len, block->pmr[chunk]->lkey,
+ block->block_name, rkey);
+}
rdma->total_registrations++;
}
diff --git a/migration/trace-events b/migration/trace-events
index 5f6aa580def..901c1d54c12 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 write 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) ""
--
2.31.1
