Date: Thu, 07 Apr 2011 13:01:53 -0700 From: Julian Elischer <julian@freebsd.org> To: Andriy Gapon <avg@freebsd.org> Cc: FreeBSD current <freebsd-current@freebsd.org> Subject: Re: prefer tsc timecounter when it's good Message-ID: <4D9E1831.4040707@freebsd.org> In-Reply-To: <4D9DF086.9020906@FreeBSD.org> References: <4D9DF086.9020906@FreeBSD.org>
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On 4/7/11 10:12 AM, Andriy Gapon wrote: > Guys, > > what do you think about the following change? > The idea is mark TSC as the best timecounter when it's invariant and synchronized > between cores. > Unfortunately I don't have code to auto-detect the synchronization and keep > relying on the corresponding tunable. I thought about auto-setting it for > single-package configurations, but even that information is currently not trivial > to get out of our mp (i386/amd64) machdep code. > > --- a/sys/x86/x86/tsc.c > +++ b/sys/x86/x86/tsc.c > @@ -169,6 +169,9 @@ init_TSC_tc(void) > printf("TSC timecounter disabled: APM enabled.\n"); > } > > + if (tsc_is_invariant) > + tsc_timecounter.tc_quality = 1200; I like this. I have to set the timecounter to TSC manually on my machines as using teh default (fast-acpi) slows my tests down by 10%-20% mind you if one were to be able to put the tunable into /boot, one could put the sysctl into /etc/sysctl.conf to do the same thing.. > + > #ifdef SMP > /* > * We can not use the TSC in SMP mode unless the TSCs on all CPUs >
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