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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1774969449; 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=F7l7nol1SzwFYWkkAmybwaQvn6WrYq0DfYyxo8Bu/rc=; b=dEDlsmUo35G3VkdAmbUlHit+B4qFc73i4kl0COgIssRZ1VSDTmB7u9KujxciW8emNhL3UC KOkbxSvM/AMaQ9igfijRFzlaWdK7R1zBHa0KlhlDTWW1aaqCYceXCmlxwmoFysX2Zdp89X mu+Xit253CoJc8t0IizakX/MWFVH0Qo= X-MC-Unique: rmiI-oJDNdKshv0HcyWhTA-1 X-Mimecast-MFC-AGG-ID: rmiI-oJDNdKshv0HcyWhTA_1774969447 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, qemu-devel@nongnu.org, peter.maydell@linaro.org Subject: [PULL 5/6] vhost-user-blk-server: fix opt_io_size=1 causing severe Windows I/O degradation Date: Tue, 31 Mar 2026 17:03:51 +0200 Message-ID: <20260331150352.256332-6-kwolf@redhat.com> In-Reply-To: <20260331150352.256332-1-kwolf@redhat.com> References: <20260331150352.256332-1-kwolf@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" From: Max Makarov The QSD vhost-user-blk export sets opt_io_size=3D1 and min_io_size=3D1 in the virtio config. These values are reported to the guest through the VPD Block Limits page as OptimalTransferLength=3D1 block (512 bytes) and OptimalTransferLengthGranularity=3D1 block. Windows respects these hints and splits all I/O into ~512-byte requests, causing ~100x sequential throughput degradation (150 MB/s instead of 15+ GB/s). Linux is unaffected as its block layer ignores these values. Set both to 0 which means "not reported" per the SCSI Block Limits VPD spec, allowing Windows to use its own optimal I/O size defaults. Signed-off-by: Max Makarov Message-ID: <20260330193451.76037-1-maxpain@linux.com> Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf --- block/export/vhost-user-blk-server.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/block/export/vhost-user-blk-server.c b/block/export/vhost-user= -blk-server.c index e89422bb85a..67912a3e170 100644 --- a/block/export/vhost-user-blk-server.c +++ b/block/export/vhost-user-blk-server.c @@ -242,8 +242,8 @@ vu_blk_initialize_config(BlockDriverState *bs, config->blk_size =3D cpu_to_le32(blk_size); config->size_max =3D cpu_to_le32(0); config->seg_max =3D cpu_to_le32(128 - 2); - config->min_io_size =3D cpu_to_le16(1); - config->opt_io_size =3D cpu_to_le32(1); + config->min_io_size =3D cpu_to_le16(0); + config->opt_io_size =3D cpu_to_le32(0); config->num_queues =3D cpu_to_le16(num_queues); config->max_discard_sectors =3D cpu_to_le32(VIRTIO_BLK_MAX_DISCARD_SECTORS); --=20 2.53.0