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block/nvme: poll queues without q->lock 

A lot of CPU time is spent simply locking/unlocking q->lock during
polling. Check for completion outside the lock to make q->lock disappear
from the profile.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Sergio Lopez <slp@redhat.com>
Message-id: 20200617132201.1832152-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2020-06-17 14:21:55 +01:00
parent d6d1a65cca
commit 2446e0e2e9
1 changed files with 12 additions and 0 deletions
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12
block/nvme.c
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@ -512,6 +512,18 @@ static bool nvme_poll_queues(BDRVNVMeState *s)
for (i = 0; i < s->nr_queues; i++) {
NVMeQueuePair *q = s->queues[i];
const size_t cqe_offset = q->cq.head * NVME_CQ_ENTRY_BYTES;
NvmeCqe *cqe = (NvmeCqe *)&q->cq.queue[cqe_offset];
/*
* Do an early check for completions. q->lock isn't needed because
* nvme_process_completion() only runs in the event loop thread and
* cannot race with itself.
*/
if ((le16_to_cpu(cqe->status) & 0x1) == q->cq_phase) {
continue;
}
qemu_mutex_lock(&q->lock);
while (nvme_process_completion(s, q)) {
/* Keep polling */