linux-kernel - Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk

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Message-ID: <4FF63954.5040408@redhat.com>
Date:	Fri, 06 Jul 2012 09:03:16 +0800
From:	Asias He <asias@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Sasha Levin <levinsasha928@...il.com>, dlaor@...hat.com,
	kvm@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk

On 07/04/2012 10:40 AM, Rusty Russell wrote:
> On Tue, 03 Jul 2012 08:39:39 +0800, Asias He <asias@...hat.com> wrote:
>> On 07/02/2012 02:41 PM, Rusty Russell wrote:
>>> Sure, our guest merging might save us 100x as many exits as no merging.
>>> But since we're not doing many requests, does it matter?
>>
>> We can still have many requests with slow devices. The number of
>> requests depends on the workload in guest. E.g. 512 IO threads in guest
>> keeping doing IO.
>
> You can have many requests outstanding.  But if the device is slow, the
> rate of requests being serviced must be low.

Yes.

> Am I misunderstanding something?  I thought if you could have a high
> rate of requests, it's not a slow device.

Sure.

-- 
Asias


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