From: Asias He <asias.hejun@gmail.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>,
Cyrill Gorcunov <gorcunov@gmail.com>, Ingo Molnar <mingo@elte.hu>,
Prasad Joshi <prasadjoshi124@gmail.com>,
kvm@vger.kernel.org
Subject: Re: [PATCH 1/2] kvm tools: Bring VIRTIO_BLK_F_SEG_MAX feature back to virtio blk
Date: Sat, 14 May 2011 00:16:08 +0800 [thread overview]
Message-ID: <4DCD5948.6090502@gmail.com> (raw)
In-Reply-To: <1305300399.25256.20.camel@lappy>
On 05/13/2011 11:26 PM, Sasha Levin wrote:
> On Fri, 2011-05-13 at 22:34 +0800, Asias He wrote:
>> On 05/13/2011 10:07 PM, Sasha Levin wrote:
>>> On Fri, 2011-05-13 at 15:46 +0300, Pekka Enberg wrote:
>>>> On 5/13/11 5:40 AM, Asias He wrote:
>>>>> commit b764422bb0b46b00b896f6d4538ac3d3dde9e56b
>>>>> (kvm tools: Add support for multiple virtio-blk)
>>>>> removed the VIRTIO_BLK_F_SEG_MAX publishment to guest.
>>>>>
>>>>> There is no reason we should not support it. Just bring it back.
>>>>>
>>>>> Signed-off-by: Asias He<asias.hejun@gmail.com>
>>>>
>>>> Sasha?
>>>
>>> I'm not sure why it was removed, must have missed it when updating
>>> struct blk_dev.
>>>
>>> On the other hand, why do we need to limit max segment size?
>>
>> That's because the number of entries in a scatter-gather operation must
>> be less than the entries in the virt queue we can offer.
>>
>
> I thought that since it's the guest who allocates vq buffers and it's
> the guest who does the sg ops, it won't attempt to do that.
The size of the virt queue (number of entries) is determined by the
device (host).
>
> But if thats the concern, then yes - lets add it to be safe.
>
--
Best Regards,
Asias He
prev parent reply other threads:[~2011-05-13 16:17 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-13 2:40 [PATCH 1/2] kvm tools: Bring VIRTIO_BLK_F_SEG_MAX feature back to virtio blk Asias He
2011-05-13 2:40 ` [PATCH 2/2] kvm tools: Tune the command-line option Asias He
2011-05-13 12:46 ` [PATCH 1/2] kvm tools: Bring VIRTIO_BLK_F_SEG_MAX feature back to virtio blk Pekka Enberg
2011-05-13 14:07 ` Sasha Levin
2011-05-13 14:34 ` Asias He
2011-05-13 15:26 ` Sasha Levin
2011-05-13 16:16 ` Asias He [this message]
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