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

["Ding, Xuan" <xuan.ding@intel.com>]

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.

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.

Regards,
Xuan

> 
> > Thanks,
> > Chenbo
> >
> 
> Thanks,
> Maxime