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bh=QqQP2gEWiHT1RhvkO6A6rp0yPTnbuodhCHyBJ6H7YKQ=; b=RyegRFRkOHxneAmOZH2kxbbC7ggeAjhGG2GL9QaBuDCrJspE4aEsu/5YLHCp4aZARNDWRD EWWlJfbVcIfEdNEuRteqOkbiK3t6Hk0/kz+OfsuCCYBSOaT7mRg4GbTvOOLhYKSGb8mJVS fOq531XMB9jw/maLXykyVfqZrnjZB34= X-MC-Unique: 6ArE6UUoOj-WBPTaYoCVug-1 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH 1/7] block/nvme: poll queues without q->lock Date: Tue, 19 May 2020 18:11:32 +0100 Message-Id: <20200519171138.201667-2-stefanha@redhat.com> In-Reply-To: <20200519171138.201667-1-stefanha@redhat.com> References: <20200519171138.201667-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=205.139.110.120; 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charset="utf-8" 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 --- block/nvme.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/block/nvme.c b/block/nvme.c index eb2f54dd9d..7eb4512666 100644 --- a/block/nvme.c +++ b/block/nvme.c @@ -512,6 +512,18 @@ static bool nvme_poll_queues(BDRVNVMeState *s) =20 for (i =3D 0; i < s->nr_queues; i++) { NVMeQueuePair *q =3D s->queues[i]; + const size_t cqe_offset =3D q->cq.head * NVME_CQ_ENTRY_BYTES; + NvmeCqe *cqe =3D (NvmeCqe *)&q->cq.queue[cqe_offset]; + + /* + * q->lock isn't needed for checking completion because + * nvme_process_completion() only runs in the event loop thread and + * cannot race with itself. + */ + if ((le16_to_cpu(cqe->status) & 0x1) =3D=3D q->cq_phase) { + continue; + } + qemu_mutex_lock(&q->lock); while (nvme_process_completion(s, q)) { /* Keep polling */ --=20 2.25.3