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vhost: remove unnecessary membarrier on I/O completion

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We've recently switched from manually calling eventfd_write()
to rte_vhost_vring_call(), which besides writing to the
eventfd, always calls a full memory barrier in the upstream
rte_vhost lib. With upstream rte_vhost we're actually
calling two memory barriers on I/O completion - one in
spdk code, one inside rte_vhost_vring_call().

The spdk barrier was only required for our internal rte_vhost
lib, whose rte_vhost_vring_call() implementation (that we
wrote) did not have such membarrier inside. So now we'll
add this membarrier there, and remove the same barrier
from spdk code.

This doesn't change any code flow for the internal rte_vhost
lib, but optimizes I/O path for the upstream version.

Change-Id: I68738d7feb9159f718b0e60ac7eed1fafd4836b9
Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/466037
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Vitaliy Mysak <vitaliy.mysak@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
This commit is contained in:
Darek Stojaczyk 2019-07-20 11:02:29 +02:00 committed by Ben Walker
parent 0ddcc49d8a
commit 3b6f69c8f5
2 changed files with 7 additions and 7 deletions
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7
lib/vhost/rte_vhost/vhost.c
View File

@ -521,6 +521,13 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
if (!vq)
return -1;
/* Ensure all our used ring changes are visible to the guest at the time
* of interrupt.
* TODO: this is currently an sfence on x86. For other architectures we
* will most likely need an smp_mb(), but smp_mb() is an overkill for x86.
*/
rte_wmb();
if (vq->callfd != -1) {
eventfd_write(vq->callfd, (eventfd_t)1);
return 0;

7
lib/vhost/vhost.c
View File

@ -463,13 +463,6 @@ spdk_vhost_vq_used_ring_enqueue(struct spdk_vhost_session *vsession,
* (volatile uint16_t *) &used->idx = virtqueue->last_used_idx;
spdk_vhost_log_used_vring_idx(vsession, virtqueue);
/* Ensure all our used ring changes are visible to the guest at the time
* of interrupt.
* TODO: this is currently an sfence on x86. For other architectures we
* will most likely need an smp_mb(), but smp_mb() is an overkill for x86.
*/
spdk_wmb();
virtqueue->used_req_cnt++;
}