From 2446e0e2e9c9aaa5f8e8c7ef9a41fe8516054831 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 17 Jun 2020 14:21:55 +0100 Subject: [PATCH] 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 Reviewed-by: Sergio Lopez Message-id: 20200617132201.1832152-2-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi --- 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 */ -- 2.30.2