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[PATCH v2 1/7] block/nvme: poll queues without q->lock
From: |
Stefan Hajnoczi |
Subject: |
[PATCH v2 1/7] block/nvme: poll queues without q->lock |
Date: |
Wed, 17 Jun 2020 14:21:55 +0100 |
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>
---
block/nvme.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/block/nvme.c b/block/nvme.c
index eb2f54dd9d..e4375ec245 100644
--- a/block/nvme.c
+++ b/block/nvme.c
@@ -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 */
--
2.26.2
- [PATCH v2 0/7] block/nvme: support nested aio_poll(), Stefan Hajnoczi, 2020/06/17
- [PATCH v2 1/7] block/nvme: poll queues without q->lock,
Stefan Hajnoczi <=
- [PATCH v2 2/7] block/nvme: drop tautologous assertion, Stefan Hajnoczi, 2020/06/17
- [PATCH v2 3/7] block/nvme: don't access CQE after moving cq.head, Stefan Hajnoczi, 2020/06/17
- [PATCH v2 4/7] block/nvme: switch to a NVMeRequest freelist, Stefan Hajnoczi, 2020/06/17
- [PATCH v2 5/7] block/nvme: clarify that free_req_queue is protected by q->lock, Stefan Hajnoczi, 2020/06/17
- [PATCH v2 6/7] block/nvme: keep BDRVNVMeState pointer in NVMeQueuePair, Stefan Hajnoczi, 2020/06/17
- [PATCH v2 7/7] block/nvme: support nested aio_poll(), Stefan Hajnoczi, 2020/06/17
- Re: [PATCH v2 0/7] block/nvme: support nested aio_poll(), Stefan Hajnoczi, 2020/06/23