linux-kernel - Re: [PATCH v3 3/3] vhost: Improve vhost_get_avail_idx() with smp

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Date: Sat, 30 Mar 2024 19:02:11 +1000
From: Gavin Shan <gshan@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
 jasowang@...hat.com, will@...nel.org, davem@...emloft.net,
 stefanha@...hat.com, sgarzare@...hat.com, keirf@...gle.com,
 yihyu@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH v3 3/3] vhost: Improve vhost_get_avail_idx() with
 smp_rmb()

On 3/28/24 19:31, Michael S. Tsirkin wrote:
> On Thu, Mar 28, 2024 at 10:21:49AM +1000, Gavin Shan wrote:
>> All the callers of vhost_get_avail_idx() are concerned to the memory
>> barrier, imposed by smp_rmb() to ensure the order of the available
>> ring entry read and avail_idx read.
>>
>> Improve vhost_get_avail_idx() so that smp_rmb() is executed when
>> the avail_idx is advanced. With it, the callers needn't to worry
>> about the memory barrier.
>>
>> Suggested-by: Michael S. Tsirkin <mst@...hat.com>
>> Signed-off-by: Gavin Shan <gshan@...hat.com>
> 
> Previous patches are ok. This one I feel needs more work -
> first more code such as sanity checking should go into
> this function, second there's actually a difference
> between comparing to last_avail_idx and just comparing
> to the previous value of avail_idx.
> I will pick patches 1-2 and post a cleanup on top so you can
> take a look, ok?
> 

Thanks, Michael. It's fine to me.

Thanks,
Gavin