> -----Original Message----- > From: Michael S. Tsirkin <m...@redhat.com> > Sent: Tuesday, July 16, 2024 12:24 AM > To: Liu, Yuan1 <yuan1....@intel.com> > Cc: Wang, Yichen <yichen.w...@bytedance.com>; Paolo Bonzini > <pbonz...@redhat.com>; Marc-André Lureau <marcandre.lur...@redhat.com>; > Daniel P. Berrangé <berra...@redhat.com>; Thomas Huth <th...@redhat.com>; > Philippe Mathieu-Daudé <phi...@linaro.org>; Peter Xu <pet...@redhat.com>; > Fabiano Rosas <faro...@suse.de>; Eric Blake <ebl...@redhat.com>; Markus > Armbruster <arm...@redhat.com>; Cornelia Huck <coh...@redhat.com>; qemu- > de...@nongnu.org; Hao Xiang <hao.xi...@linux.dev>; Kumar, Shivam > <shivam.kum...@nutanix.com>; Ho-Ren (Jack) Chuang > <horenchu...@bytedance.com> > 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
