Date: Sat, 25 Apr 2015 10:18:50 -0700 From: "K. Macy" <kmacy@freebsd.org> To: Adrian Chadd <adrian@freebsd.org> Cc: "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: RFC: setting performance_cx_lowest=C2 in -HEAD to avoid lock contention on many-CPU boxes Message-ID: <CAHM0Q_NuvZH0GGs-J9xniyt2PZ0qb_kjOaanVOaCxzD0CVzGYg@mail.gmail.com> In-Reply-To: <CAJ-VmonG%2By5gzoYmer70KAswUorvezcZxRSDsQWj47=jsAZ71w@mail.gmail.com> References: <CAJ-VmonG%2By5gzoYmer70KAswUorvezcZxRSDsQWj47=jsAZ71w@mail.gmail.com>
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Perhaps use an arbitrary cutoff - say <= 8 cores - where the cx_lowest=C3. This serialization isn't going to hurt on systems with more modest core counts. On Sat, Apr 25, 2015 at 9:31 AM, Adrian Chadd <adrian@freebsd.org> wrote: > Hi! > > I've been doing some NUMA testing on large boxes and I've found that > there's lock contention in the ACPI path. It's due to my change a > while ago to start using sleep states above ACPI C1 by default. The > ACPI C3 state involves a bunch of register fiddling in the ACPI sleep > path that grabs a serialiser lock, and on an 80 thread box this is > costly. > > I'd like to drop performance_cx_lowest to C2 in -HEAD. ACPI C2 state > doesn't require the same register fiddling (to disable bus mastering, > if I'm reading it right) and so it doesn't enter that particular > serialised path. I've verified on Westmere-EX, Sandybridge, Ivybridge > and Haswell boxes that ACPI C2 does let one drop down into a deeper > CPU sleep state (C6 on each of these). I think is still a good default > for both servers and desktops. > > If no-one has a problem with this then I'll do it after the weekend. > > Thanks! > > > > -adrian > _______________________________________________ > freebsd-arch@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org"
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