From: Christoph Hellwig <hch@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>,
Minchan Kim <minchan@kernel.org>,
Rusty Russell <rusty@rustcorp.com.au>,
Chris Wright <chrisw@sous-sol.org>, Jens Axboe <axboe@kernel.dk>,
Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Christoph Hellwig <hch@infradead.org>,
Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH 0/6][RFC] virtio-blk: Change I/O path from request to BIO
Date: Mon, 2 Jan 2012 11:15:18 -0500 [thread overview]
Message-ID: <20120102161518.GA28940@infradead.org> (raw)
In-Reply-To: <4F01D750.7040304@redhat.com>
On Mon, Jan 02, 2012 at 05:12:00PM +0100, Paolo Bonzini wrote:
> On 01/01/2012 05:45 PM, Stefan Hajnoczi wrote:
> >By the way, drivers for solid-state devices can set QUEUE_FLAG_NONROT
> >to hint that seek time optimizations may be sub-optimal. NBD and
> >other virtual/pseudo device drivers set this flag. Should virtio-blk
> >set it and how does it affect performance?
>
> By itself is not a good idea in general.
>
> When QEMU uses O_DIRECT, the guest should not use QUEUE_FLAG_NONROT
> unless it is active for the host disk as well. (In doubt, as is the
> case for remote hosts accessed over NFS, I would also avoid NONROT
> and allow more coalescing).
Do we have any benchmark numbers where QUEUE_FLAG_NONROT makes a
difference? I tried a few times, and the only constant measureable
thing was that it regressed performance when used for rotating devices
in a few benchmarks.
next prev parent reply other threads:[~2012-01-02 16:15 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-21 1:00 [PATCH 0/6][RFC] virtio-blk: Change I/O path from request to BIO Minchan Kim
2011-12-21 1:00 ` [PATCH 1/6] block: add bio_map_sg Minchan Kim
2011-12-21 1:00 ` [PATCH 2/6] virtio: support unlocked queue kick Minchan Kim
2011-12-21 1:00 ` [PATCH 3/6] virtio-blk: remove the unused list of pending requests Minchan Kim
2011-12-21 1:00 ` [PATCH 4/6] virtio-blk: implement ->make_request Minchan Kim
2011-12-22 12:20 ` Stefan Hajnoczi
2011-12-22 20:28 ` Christoph Hellwig
2011-12-21 1:00 ` [PATCH 5/6] virtio-blk: Support batch I/O for enhancing sequential IO Minchan Kim
2011-12-21 1:00 ` [PATCH 6/6] virtio-blk: Emulate Flush/FUA Minchan Kim
2011-12-21 5:08 ` [PATCH 0/6][RFC] virtio-blk: Change I/O path from request to BIO Rusty Russell
2011-12-21 5:56 ` Minchan Kim
2011-12-21 8:28 ` Sasha Levin
2011-12-21 8:17 ` Minchan Kim
2011-12-21 19:11 ` Vivek Goyal
2011-12-22 1:05 ` Minchan Kim
2011-12-22 15:45 ` Vivek Goyal
2011-12-22 23:26 ` Minchan Kim
2011-12-22 12:57 ` Stefan Hajnoczi
2011-12-22 23:41 ` Minchan Kim
2012-01-01 16:45 ` Stefan Hajnoczi
2012-01-02 7:48 ` Dor Laor
2012-01-02 16:12 ` Paolo Bonzini
2012-01-02 16:15 ` Christoph Hellwig [this message]
2012-01-02 16:18 ` Paolo Bonzini
2012-01-02 16:23 ` Christoph Hellwig
2012-01-02 16:18 ` Christoph Hellwig
2012-01-02 16:21 ` Avi Kivity
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