linux-kernel - Re: [PATCHv2] vhost-net: utilize PUBLISH_USED

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Message-ID: <4BF40E8D.7020409@redhat.com>
Date:	Wed, 19 May 2010 19:15:09 +0300
From:	Avi Kivity <avi@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	davem@...emloft.net, Juan Quintela <quintela@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Arnd Bergmann <arnd@...db.de>, kvm@...r.kernel.org,
	virtualization@...ts.osdl.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, alex.williamson@...hat.com,
	amit.shah@...hat.com
Subject: Re: [PATCHv2] vhost-net: utilize PUBLISH_USED_IDX feature

On 05/18/2010 08:47 PM, Avi Kivity wrote:
> On 05/18/2010 05:21 AM, Michael S. Tsirkin wrote:
>> With PUBLISH_USED_IDX, guest tells us which used entries
>> it has consumed. This can be used to reduce the number
>> of interrupts: after we write a used entry, if the guest has not yet
>> consumed the previous entry, or if the guest has already consumed the
>> new entry, we do not need to interrupt.
>> This imporves bandwidth by 30% under some workflows.
>
> Seems to be missing the cacheline alignment.
>
> Rusty's clarification did not satisfy me, I think it's needed.
>

Oh, and this should definitely follow the patch to the virtio spec, not 
precede it.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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