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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1753390036; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yw5wu0Bvtn1lGx974paDUSobpem7+N41X/8z4DQO0zY=; b=hlelHWjR4MqBx82LFrhMPT6m0Iw2dnfOC+vfLDQO9XUMobgfSlXs3PgJY32YftevNv0EU6 f2Thd/8koaqKRG4CIt/eBK01E4ohMvDWrMzNGEdws8ko7rXheB4GeB7QsyDMYmOa9Cbx7f d7wapr+qNmdcaxyoifJktXS4xWxOmSo= X-MC-Unique: zpkpmTvyPo6-XBMwd0zDPQ-1 X-Mimecast-MFC-AGG-ID: zpkpmTvyPo6-XBMwd0zDPQ_1753390031 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Stefan Hajnoczi , Brian Song , qemu-block@nongnu.org, Bernd Schubert , Kevin Wolf , h0lyalg0rithm@git.sr.ht, Fam Zheng Subject: [RFC 2/3] aio-posix: enable IORING_SETUP_SINGLE_ISSUER Date: Thu, 24 Jul 2025 16:47:01 -0400 Message-ID: <20250724204702.576637-3-stefanha@redhat.com> In-Reply-To: <20250724204702.576637-1-stefanha@redhat.com> References: <20250724204702.576637-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" IORING_SETUP_SINGLE_ISSUER enables optimizations in the host Linux kernel's io_uring code when the io_uring context is only used from a single thread. This is true is QEMU because io_uring SQEs are submitted from the same thread that processes the CQEs. Signed-off-by: Stefan Hajnoczi --- util/fdmon-io_uring.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c index 28b93c8ab9..4798439097 100644 --- a/util/fdmon-io_uring.c +++ b/util/fdmon-io_uring.c @@ -456,13 +456,30 @@ static const FDMonOps fdmon_io_uring_ops =3D { .add_sqe =3D fdmon_io_uring_add_sqe, }; =20 +static inline bool is_creating_iothread(void) +{ + return qemu_get_thread_id() !=3D getpid(); +} + void fdmon_io_uring_setup(AioContext *ctx, Error **errp) { int ret; + /* TODO only enable these flags if they are available in the host's ke= rnel headers */ + unsigned flags =3D 0; =20 ctx->io_uring_fd_tag =3D NULL; =20 - ret =3D io_uring_queue_init(FDMON_IO_URING_ENTRIES, &ctx->fdmon_io_uri= ng, 0); + /* + * The main thread's AioContexts are created from the main loop thread= but + * may be accessed from multiple threads (e.g. vCPUs or the migration + * thread). IOThread AioContexts are only accessed from the IOThread + * itself. + */ + if (is_creating_iothread()) { + flags =3D IORING_SETUP_SINGLE_ISSUER; + } + + ret =3D io_uring_queue_init(FDMON_IO_URING_ENTRIES, &ctx->fdmon_io_uri= ng, flags); if (ret !=3D 0) { error_setg_errno(errp, -ret, "Failed to initialize io_uring"); return; --=20 2.50.1