> -----Original Message----- > From: Michael S. Tsirkin <[email protected]> > Sent: Tuesday, July 16, 2024 12:24 AM > To: Liu, Yuan1 <[email protected]> > Cc: Wang, Yichen <[email protected]>; Paolo Bonzini > <[email protected]>; Marc-André Lureau <[email protected]>; > Daniel P. Berrangé <[email protected]>; Thomas Huth <[email protected]>; > Philippe Mathieu-Daudé <[email protected]>; Peter Xu <[email protected]>; > Fabiano Rosas <[email protected]>; Eric Blake <[email protected]>; Markus > Armbruster <[email protected]>; Cornelia Huck <[email protected]>; qemu- > [email protected]; Hao Xiang <[email protected]>; Kumar, Shivam > <[email protected]>; Ho-Ren (Jack) Chuang > <[email protected]> > Subject: Re: [PATCH v5 00/13] WIP: Use Intel DSA accelerator to offload > zero page checking in multifd live migration. > > On Mon, Jul 15, 2024 at 03:57:42PM +0000, Liu, Yuan1 wrote: > > > > > > > > > that is 23% total CPU usage savings. > > > > > > > > > > > > > > > > > > > > > > > > Here the DSA was mostly idle. > > > > > > > > > > > > > > > > Sounds good but a question: what if several qemu instances > are > > > > > > > > migrated in parallel? > > > > > > > > > > > > > > > > Some accelerators tend to basically stall if several tasks > > > > > > > > are trying to use them at the same time. > > > > > > > > > > > > > > > > Where is the boundary here? > > > > If I understand correctly, you are concerned that in some scenarios the > > accelerator itself is the migration bottleneck, causing the migration > performance > > to be degraded. > > > > My understanding is to make full use of the accelerator bandwidth, and > once > > the accelerator is the bottleneck, it will fall back to zero-page > detection > > by the CPU. > > > > For example, when the enqcmd command returns an error which means the > work queue > > is full, then we can add some retry mechanisms or directly use CPU > detection. > > > How is it handled in your patch? If you just abort migration unless > enqcmd succeeds then would that not be a bug, where loading the system > leads to migraton failures?
Sorry for this, I have just started reviewing this patch. The content we discussed before is only related to the DSA device itself and may not be related to this patch's implementation. I will review the issue you mentioned carefully. Thank you for your reminder. > -- > MST
