Re: [PATCH] vhost: fix unnecessary dirty page logging

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi,

On 7/8/22 09:04, Ding, Xuan wrote:
> Hi,
> 
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: 2022年7月7日 19:31
>> To: Xia, Chenbo <chenbo.xia@intel.com>; Ding, Xuan <xuan.ding@intel.com>
>> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; He, Xingguang
>> <xingguang.he@intel.com>; Yang, YvonneX <yvonnex.yang@intel.com>; Jiang,
>> Cheng1 <cheng1.jiang@intel.com>
>> Subject: Re: [PATCH] vhost: fix unnecessary dirty page logging
>>
>>
>>
>> On 7/7/22 11:51, Xia, Chenbo wrote:
>>>> -----Original Message-----
>>>> From: Ding, Xuan <xuan.ding@intel.com>
>>>> Sent: Thursday, July 7, 2022 2:55 PM
>>>> To: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
>>>> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; He, Xingguang
>>>> <xingguang.he@intel.com>; Yang, YvonneX <yvonnex.yang@intel.com>;
>>>> Jiang,
>>>> Cheng1 <cheng1.jiang@intel.com>; Ding, Xuan <xuan.ding@intel.com>
>>>> Subject: [PATCH] vhost: fix unnecessary dirty page logging
>>>>
>>>> From: Xuan Ding <xuan.ding@intel.com>
>>>>
>>>> The dirty page logging is only required in vhost enqueue direction
>>>> for live migration. This patch removes the unnecessary dirty page
>>>> logging in vhost dequeue direction. Otherwise, it will result in a
>>>> performance drop. Some if-else judgements are also optimized to improve
>> performance.
>>>>
>>>> Fixes: 6d823bb302c7 ("vhost: prepare sync for descriptor to mbuf
>>>> refactoring")
>>>> Fixes: b6eee3e83402 ("vhost: fix sync dequeue offload")
>>>>
>>>> Signed-off-by: Xuan Ding <xuan.ding@intel.com>
>>>> ---
>>>
>>> Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>
>>>
>>> Although it's late in release, we can consider to merge this as I see
>>> it impacts the performance by 5%:
>>>
>> http://inbox.dpdk.org/dev/BYAPR11MB2711F13CDA2B0A4535A6591EFE839@B
>> YAPR
>>> 11MB2711.namprd11.prod.outlook.com/T/#t
>>
>> Yes, I raised we need it in -rc4 at today's Release status meeting.
>> I'll review it today.
>>
>>> But also, it will be good to know the performance issue is solved by
>>> sharing the test results.
>>
>> Yes, Intel performance results would be appreciated.
> 
> This fix patch is for the issue reported at 22.07-rc3. The refactoring patch brings a 3%~5% perf drop in vhost sync path.
> With fix patch, the perf drop introduced by refactoring is solved.

Good.

> However, the testing result shows there still exists ~5% packed ring perf drop compared with 22.03.
> We find the improving checksum offload patch series in 22.07 may contribute to the packed ring perf drop.
> Because we always do checksum checks in PMD.
> 
> Could you help to double check this patch series, is it as expected?
> Your assistance is really appreciated.

I will look again, but if your analysis is right, there's not much we
can do. The series is filling gaps in the checksum offload support.

I will not have time to work on it for v22.07, we're too late in the
cycle. What surprises me is that only packed ring is impacted.

Regards,
Maxime

> 
> Regards,
> Xuan
> 
>>
>>> Thanks,
>>> Chenbo
>>>
>>
>> Thanks,
>> Maxime
>