aboutsummaryrefslogtreecommitdiff
path: root/block
diff options
context:
space:
mode:
authorStefan Hajnoczi <stefanha@redhat.com>2020-06-17 14:21:55 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2020-06-23 15:46:08 +0100
commit2446e0e2e9c9aaa5f8e8c7ef9a41fe8516054831 (patch)
treecf7b49f174a5c6880ec9e9992c1ae86a4d5a5370 /block
parentd6d1a65ccab670788b6c30d918ac7bd636513f8e (diff)
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>
Diffstat (limited to 'block')
-rw-r--r--block/nvme.c12
1 files changed, 12 insertions, 0 deletions
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 */