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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1761837737; 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=6Lm/GnRFPdaTGn+n6ZnJEDhQJPDWu5LYL8zGrDK1Esk=; b=eI8zDAdksza/Xw7Ko8A/kI0x/qDRqDecaDDF+kMvU7pS6otchy03CbDSOn85cIp8+t8qDs PIWfXvODdGack+T1EZZC634QxAtAnjICnyqKF8VANPBHIWihRVFbIemNI0z00+ukD6B8nY 0vylGPNv/ETqpFQYM6eBnJqitg8AJF4= X-MC-Unique: o0MS5bP7PAafbh0yB6aF3A-1 X-Mimecast-MFC-AGG-ID: o0MS5bP7PAafbh0yB6aF3A_1761837733 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Hanna Czenczek , Paolo Bonzini , hibriansong@gmail.com, eblake@redhat.com, Stefan Hajnoczi , Kevin Wolf , qemu-block@nongnu.org Subject: [RESEND PATCH v5 13/13] block/io_uring: use non-vectored read/write when possible Date: Thu, 30 Oct 2025 11:21:49 -0400 Message-ID: <20251030152150.470170-14-stefanha@redhat.com> In-Reply-To: <20251030152150.470170-1-stefanha@redhat.com> References: <20251030152150.470170-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 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 --- v5: - Reduce #ifdef HAVE_IO_URING_PREP_WRITEV2 code duplication [Kevin] --- block/io_uring.c | 34 ++++++++++++++++++++++++++-------- 1 file changed, 26 insertions(+), 8 deletions(-) diff --git a/block/io_uring.c b/block/io_uring.c index dd930ee57e..f1514cf024 100644 --- a/block/io_uring.c +++ b/block/io_uring.c @@ -46,17 +46,28 @@ static void luring_prep_sqe(struct io_uring_sqe *sqe, v= oid *opaque) =20 switch (req->type) { case QEMU_AIO_WRITE: -#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) { +#ifdef HAVE_IO_URING_PREP_WRITEV2 + io_uring_prep_writev2(sqe, fd, qiov->iov, + qiov->niov, offset, luring_flags); #else - assert(flags =3D=3D 0); - io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset); + /* + * FUA should only be enabled with HAVE_IO_URING_PREP_WRITEV2,= see + * luring_has_fua(). + */ + assert(luring_flags =3D=3D 0); + + io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset); #endif + } 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); + } break; + } case QEMU_AIO_ZONE_APPEND: io_uring_prep_writev(sqe, fd, qiov->iov, qiov->niov, offset); break; @@ -65,8 +76,15 @@ 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