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Message-ID: <4AE986FE.3040104@redhat.com> Date: Thu, 29 Oct 2009 14:13:50 +0200 From: Avi Kivity <avi@...hat.com> To: Jeremy Fitzhardinge <jeremy@...p.org> CC: Glauber Costa <glommer@...hat.com>, Dan Magenheimer <dan.magenheimer@...cle.com>, Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>, kurt.hackel@...cle.com, the arch/x86 maintainers <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Glauber de Oliveira Costa <gcosta@...hat.com>, Xen-devel <xen-devel@...ts.xensource.com>, Keir Fraser <keir.fraser@...citrix.com>, zach.brown@...cle.com, chris.mason@...cle.com, Ingo Molnar <mingo@...hat.com> Subject: Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation On 10/28/2009 07:47 PM, Jeremy Fitzhardinge wrote: >> Much better to have an API for this. Life is hacky enough already. >> > My point is that if an app cares about property X then it should just > measure property X. The fact that gettimeofday is a vsyscall is just an > implementation detail that apps don't really care about. What they care > about is whether gettimeofday is fast or not. > But we can not make a reliable measurement. > If the environment has such unstable timing that the effect can't be > measured, then it is moot whether its a vsyscall or not (but in that > case its almost certainly better to use the standard API rather than > trying to roll your own timesource with rdtsc). > If you're interested in gettimeofday() for a global monotonic counter you can fall back to atomic_fetch_and_add() which will be faster than a syscall even on large systems. Maybe we should provide a vsyscall for global monotonic counters and implement it using a atomics or tsc instead of these hacks (I'm assuming here that the gettimeofday() calls are used to implement an atomic counter - are they?) -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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