On 17/09/2021 10:27, Julien Grall wrote: > Hi, > > (+ some AWS folks) > > On 17/09/2021 11:17, Jan Beulich wrote: >> On 16.09.2021 19:52, Andrew Cooper wrote: >>> On 16/09/2021 13:30, Jan Beulich wrote: >>>> On 16.09.2021 13:10, Dmitry Isaikin wrote: >>>>> From: Dmitry Isaykin <[email protected]> >>>>> >>>>> This significantly speeds up concurrent destruction of multiple >>>>> domains on x86. >>>> This effectively is a simplistic revert of 228ab9992ffb ("domctl: >>>> improve locking during domain destruction"). There it was found to >>>> actually improve things; >>> >>> Was it? I recall that it was simply an expectation that performance >>> would be better... >> >> My recollection is that it was, for one of our customers. >> >>> Amazon previously identified 228ab9992ffb as a massive perf hit, too. >> >> Interesting. I don't recall any mail to that effect. > > Here we go: > > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fxen-devel%2Fde46590ad566d9be55b26eaca0bc4dc7fbbada59.1585063311.git.hongyxia%40amazon.com%2F&data=04%7C01%7CAndrew.Cooper3%40citrix.com%7C8cf65b3fb3324abe7cf108d979bd7171%7C335836de42ef43a2b145348c2ee9ca5b%7C0%7C0%7C637674676843910175%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=si7eYIxSqsJY77sWuwsad5MzJDMzGF%2F8L0JxGrWTmtI%3D&reserved=0 > > > We have been using the revert for quite a while in production and didn't > notice any regression. > >> >>> Clearly some of the reasoning behind 228ab9992ffb was flawed and/or >>> incomplete, and it appears as if it wasn't necessarily a wise move in >>> hindsight. >> >> Possible; I continue to think though that the present observation wants >> properly understanding instead of more or less blindly undoing that >> change. > > To be honest, I think this is the other way around. You wrote and merged > a patch with the following justification: > > " > There is no need to hold the global domctl lock across domain_kill() - > the domain lock is fully sufficient here, and parallel cleanup after > multiple domains performs quite a bit better this way. > " > > Clearly, the original commit message is lacking details on the exact > setups and numbers. But we now have two stakeholders with proof that > your patch is harmful to the setup you claim perform better with your > patch. > > To me this is enough justification to revert the original patch. Anyone > against the revert, should provide clear details of why the patch should > not be reverted.
I second a revert. I was concerned at the time that the claim was unsubstantiated, and now there is plenty of evidence to counter the claim. ~Andrew
