From: Paolo Bonzini <pbonzini@redhat.com>
To: dlaor@redhat.com
Cc: Ronen Hod <rhod@redhat.com>,
kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk
Date: Wed, 04 Jul 2012 16:10:40 +0200 [thread overview]
Message-ID: <4FF44EE0.9040200@redhat.com> (raw)
In-Reply-To: <4FF3017C.4020605@redhat.com>
Il 03/07/2012 16:28, Dor Laor ha scritto:
>>>> Users using a spinning disk still get IO scheduling in the host though.
>>>> What benefit is there in doing it in the guest as well?
>>>
>>> The io scheduler waits for requests to merge and thus batch IOs
>>> together. It's not important w.r.t spinning disks since the host can
>>> do it but it causes much less vmexits which is the key issue for VMs.
>>
>> Does it make sense to use the guest's I/O scheduler at all?
>
> That's the reason we have a noop io scheduler.
But is performance really better with noop? We had to revert usage of
QUEUE_FLAG_NONROT in the guests because it caused performance
degradation (commit f8b12e513b953aebf30f8ff7d2de9be7e024dbbe).
The bio-based path is really QUEUE_FLAG_NONROT++, so it should really be
a special case for people who know what they're doing. (Better would be
to improve QEMU, there's definitely room for 20% improvement...).
Paolo
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: dlaor@redhat.com
Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Ronen Hod <rhod@redhat.com>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk
Date: Wed, 04 Jul 2012 16:10:40 +0200 [thread overview]
Message-ID: <4FF44EE0.9040200@redhat.com> (raw)
In-Reply-To: <4FF3017C.4020605@redhat.com>
Il 03/07/2012 16:28, Dor Laor ha scritto:
>>>> Users using a spinning disk still get IO scheduling in the host though.
>>>> What benefit is there in doing it in the guest as well?
>>>
>>> The io scheduler waits for requests to merge and thus batch IOs
>>> together. It's not important w.r.t spinning disks since the host can
>>> do it but it causes much less vmexits which is the key issue for VMs.
>>
>> Does it make sense to use the guest's I/O scheduler at all?
>
> That's the reason we have a noop io scheduler.
But is performance really better with noop? We had to revert usage of
QUEUE_FLAG_NONROT in the guests because it caused performance
degradation (commit f8b12e513b953aebf30f8ff7d2de9be7e024dbbe).
The bio-based path is really QUEUE_FLAG_NONROT++, so it should really be
a special case for people who know what they're doing. (Better would be
to improve QEMU, there's definitely room for 20% improvement...).
Paolo
next prev parent reply other threads:[~2012-07-04 14:10 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-18 6:53 [PATCH v2 0/3] Improve virtio-blk performance Asias He
2012-06-18 6:53 ` Asias He
2012-06-18 6:53 ` [PATCH 1/3] block: Introduce __blk_segment_map_sg() helper Asias He
2012-06-18 6:53 ` Asias He
2012-06-18 21:31 ` Tejun Heo
2012-06-18 21:31 ` Tejun Heo
2012-06-19 2:02 ` Asias He
2012-06-19 2:02 ` Asias He
2012-06-19 18:00 ` Tejun Heo
2012-06-19 18:00 ` Tejun Heo
2012-06-18 6:53 ` [PATCH v2 2/3] block: Add blk_bio_map_sg() helper Asias He
2012-06-18 6:53 ` Asias He
2012-06-18 6:53 ` [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk Asias He
2012-06-18 6:53 ` Asias He
2012-06-18 7:46 ` Rusty Russell
2012-06-18 7:46 ` Rusty Russell
2012-06-18 8:03 ` Asias He
2012-06-18 8:03 ` Asias He
2012-06-18 10:05 ` Rusty Russell
2012-06-18 10:05 ` Rusty Russell
2012-06-18 11:14 ` Dor Laor
2012-06-18 11:14 ` Dor Laor
2012-06-18 11:39 ` Sasha Levin
2012-06-18 11:39 ` Sasha Levin
2012-06-19 2:51 ` Asias He
2012-06-19 2:51 ` Asias He
2012-06-19 6:21 ` Dor Laor
2012-06-19 6:21 ` Dor Laor
2012-06-20 4:46 ` Asias He
2012-06-20 4:46 ` Asias He
2012-06-21 9:49 ` Dor Laor
2012-06-21 9:49 ` Dor Laor
2012-07-01 23:54 ` Rusty Russell
2012-07-02 2:45 ` Asias He
2012-07-02 2:45 ` Asias He
2012-07-02 6:41 ` Rusty Russell
2012-07-02 6:41 ` Rusty Russell
2012-07-03 0:39 ` Asias He
2012-07-03 0:39 ` Asias He
2012-07-04 2:40 ` Rusty Russell
2012-07-04 2:40 ` Rusty Russell
2012-07-06 1:03 ` Asias He
2012-07-06 1:03 ` Asias He
2012-07-03 13:31 ` Paolo Bonzini
2012-07-03 13:31 ` Paolo Bonzini
2012-07-03 14:02 ` Asias He
2012-07-03 14:02 ` Asias He
2012-07-01 23:54 ` Rusty Russell
2012-07-03 14:22 ` Ronen Hod
2012-07-03 14:22 ` Ronen Hod
2012-07-03 14:28 ` Dor Laor
2012-07-03 14:28 ` Dor Laor
2012-07-04 14:10 ` Paolo Bonzini [this message]
2012-07-04 14:10 ` Paolo Bonzini
2012-06-18 21:28 ` Tejun Heo
2012-06-18 21:28 ` Tejun Heo
2012-06-19 2:39 ` Asias He
2012-06-19 2:39 ` Asias He
2012-06-18 10:13 ` Michael S. Tsirkin
2012-06-18 10:13 ` Michael S. Tsirkin
2012-06-19 2:21 ` Asias He
2012-06-19 2:21 ` Asias He
2012-06-18 9:37 ` Stefan Hajnoczi
2012-06-18 9:37 ` Stefan Hajnoczi
2012-06-18 10:21 ` Michael S. Tsirkin
2012-06-18 10:21 ` Michael S. Tsirkin
2012-06-18 10:45 ` Stefan Hajnoczi
2012-06-18 10:45 ` Stefan Hajnoczi
2012-06-19 2:30 ` Asias He
2012-06-19 2:30 ` Asias He
2012-06-18 9:14 ` [PATCH v2 0/3] Improve virtio-blk performance Stefan Hajnoczi
2012-06-18 9:14 ` Stefan Hajnoczi
2012-06-18 9:39 ` Asias He
2012-06-18 9:39 ` Asias He
2012-06-18 10:58 ` Stefan Hajnoczi
2012-06-18 10:58 ` Stefan Hajnoczi
2012-06-19 4:24 ` Asias He
2012-06-19 4:24 ` Asias He
2012-06-19 10:14 ` Stefan Hajnoczi
2012-06-19 10:14 ` Stefan Hajnoczi
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