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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1757527625; 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=m7ShvVxcohLryooGwoHjde/Zqt4sTaKcWehk8sb96Oo=; b=Ak05ZdTSwk/0fE7kHctvD7J64zSqOD5h64ppvy4JkZYy8vyBjfLLalpQ03Qa8AMKXmhZoj 0PacsUhFDeh7n0kSo1HFh4pCNAThKQwcAF7No4sRdhqBwyUEbCYhTJZ0JWhxpwyeoDJ6dG QkXQUqL81mUyrMJLyuCESpU4X9ZumbM= X-MC-Unique: iNFkpZrvP42qcidO9zzaaw-1 X-Mimecast-MFC-AGG-ID: iNFkpZrvP42qcidO9zzaaw_1757527620 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Aarushi Mehta , Fam Zheng , Stefano Garzarella , Hanna Czenczek , eblake@redhat.com, Stefan Hajnoczi , Kevin Wolf , qemu-block@nongnu.org, hibriansong@gmail.com, Stefan Weil , Paolo Bonzini Subject: [PATCH v4 12/12] block/io_uring: use non-vectored read/write when possible Date: Wed, 10 Sep 2025 13:57:03 -0400 Message-ID: <20250910175703.374499-13-stefanha@redhat.com> In-Reply-To: <20250910175703.374499-1-stefanha@redhat.com> References: <20250910175703.374499-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 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" The io_uring_prep_readv2/writev2() man pages recommend using the non-vectored read/write operations when possible for performance reasons. I didn't measure a significant difference but it doesn't hurt to have this optimization in place. Suggested-by: Eric Blake Signed-off-by: Stefan Hajnoczi --- block/io_uring.c | 29 ++++++++++++++++++++++++----- 1 file changed, 24 insertions(+), 5 deletions(-) diff --git a/block/io_uring.c b/block/io_uring.c index dd930ee57e..bbefbddcc0 100644 --- a/block/io_uring.c +++ b/block/io_uring.c @@ -49,12 +49,24 @@ static void luring_prep_sqe(struct io_uring_sqe *sqe, v= oid *opaque) #ifdef HAVE_IO_URING_PREP_WRITEV2 { int luring_flags =3D (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0; - io_uring_prep_writev2(sqe, fd, qiov->iov, - qiov->niov, offset, luring_flags); + if (luring_flags !=3D 0 || qiov->niov > 1) { + io_uring_prep_writev2(sqe, fd, qiov->iov, + qiov->niov, offset, luring_flags); + } else { + /* The man page says non-vectored is faster than vectored */ + struct iovec *iov =3D qiov->iov; + io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offs= et); + } } #else assert(flags =3D=3D 0); - io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset); + if (qiov->niov > 1) { + io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset); + } else { + /* The man page says non-vectored is faster than vectored */ + struct iovec *iov =3D qiov->iov; + io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len, offs= et); + } #endif break; case QEMU_AIO_ZONE_APPEND: @@ -65,8 +77,15 @@ static void luring_prep_sqe(struct io_uring_sqe *sqe, vo= id *opaque) if (req->resubmit_qiov.iov !=3D NULL) { qiov =3D &req->resubmit_qiov; } - io_uring_prep_readv(sqe, fd, qiov->iov, qiov->niov, - offset + req->total_read); + if (qiov->niov > 1) { + io_uring_prep_readv(sqe, fd, qiov->iov, qiov->niov, + offset + req->total_read); + } else { + /* The man page says non-vectored is faster than vectored */ + struct iovec *iov =3D qiov->iov; + io_uring_prep_read(sqe, fd, iov->iov_base, iov->iov_len, + offset + req->total_read); + } break; } case QEMU_AIO_FLUSH: --=20 2.51.0