lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Tue, 09 Apr 2019 19:21:54 +1000 From: Nicholas Piggin <npiggin@...il.com> To: Thomas Gleixner <tglx@...utronix.de> Cc: Frederic Weisbecker <fweisbec@...il.com>, linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, "Rafael J . Wysocki" <rafael.j.wysocki@...el.com> Subject: Re: [PATCH 0/4] Allow CPU0 to be nohz full Thomas Gleixner's on April 6, 2019 3:54 am: > On Fri, 5 Apr 2019, Nicholas Piggin wrote: >> Thomas Gleixner's on April 5, 2019 12:36 am: >> > On Thu, 4 Apr 2019, Nicholas Piggin wrote: >> > >> >> I've been looking at ways to fix suspend breakage with CPU0 as a >> >> nohz CPU. I started looking at various things like allowing CPU0 >> >> to take over do_timer again temporarily or allowing nohz full >> >> to be stopped at runtime (that is quite a significant change for >> >> little real benefit). The problem then was having the housekeeping >> >> CPU go offline. >> >> >> >> So I decided to try just allowing the freeze to occur on non-zero >> >> CPU. This seems to be a lot simpler to get working, but I guess >> >> some archs won't be able to deal with this? Would it be okay to >> >> make it opt-in per arch? >> > >> > It needs to be opt in. x86 will fall on its nose with that. >> >> Okay I can add that. >> >> > Now the real interesting question is WHY do we need that at all? >> >> Why full nohz for CPU0? Basically this is how their job system was >> written and used, testing nohz full was a change that came much later >> as an optimisation. >> >> I don't think there is a fundamental reason an equivalent system >> could not be made that uses a different CPU for housekeeping, but I >> was assured the change would be quite difficult for them. >> >> If we can support it, it seems nice if you can take a particular >> configuration and just apply nohz_full to your application processors >> without any other changes. > > This wants an explanation in the patches. Okay. > And patch 4 has in the changelog: > > nohz_full has been successful at significantly reducing jitter for a > large supercomputer customer, but their job control system requires CPU0 > to be for housekeeping. > > which just makes me dazed and confused :) > > Other than some coherent explanation and making it opt in, I don't think > there is a fundamental issue with that. I will try to make the changelogs less jibberish then :) Thanks, Nick
Powered by blists - more mailing lists