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

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Date: Tue, 23 Apr 2024 13:36:28 +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 4/23/24 06:46, Michael S. Tsirkin wrote:
> On Mon, Apr 08, 2024 at 02:15:24PM +1000, Gavin Shan wrote:
>> On 3/30/24 19:02, Gavin Shan wrote:
>>> 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.
>>>
>>
>> A kindly ping.
>>
>> If it's ok to you, could you please merge PATCH[1-2]? Our downstream
>> 9.4 need the fixes, especially for NVidia's grace-hopper and grace-grace
>> platforms.
>>
>> For PATCH[3], I also can help with the improvement if you don't have time
>> for it. Please let me know.
>>
> 
> 1-2 are upstream go ahead and post the cleanup.
> 

Michael, a cleanup series has been sent for review.

https://lore.kernel.org/virtualization/20240423032407.262329-1-gshan@redhat.com/T/#t

Thanks,
Gavin