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

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

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: 2022年7月8日 15:58
> To: Ding, Xuan <xuan.ding@intel.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>
> Subject: Re: [PATCH] vhost: fix unnecessary dirty page logging
> 
> 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.
 
Yes, I think so.

> 
> 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.
 
From the testing results, the packed ring is more sensitive to the patch series,
while split ring shows a much lower drop in performance.

Thanks for your support!

Regards,
Xuan

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