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Message-Id: <1166889227.14081.13.camel@imap.mvista.com> Date: Sat, 23 Dec 2006 07:53:47 -0800 From: Daniel Walker <dwalker@...sta.com> To: eranian@....hp.com Cc: linux-kernel@...r.kernel.org, venkatesh.pallipadi@...el.com, suresh.b.siddha@...el.com, kenneth.w.chen@...el.com, tony.luck@...el.com Subject: Re: sched_clock() on i386 On Fri, 2006-12-22 at 02:43 -0800, Stephane Eranian wrote: > Hello, > > > The perfmon subsystems needs to compute per-CPU duration. It is using > sched_clock() to provide this information. However, it seems they are > big variations in the way sched_clock() is implemented for each architectures, > especially in the accuracy of the returned value (going from TSC to jiffies). > The vast majority of architectures return a scaled jiffies value for sched_clock(). MIPS, and ARM for instance are two, and i386 does sometimes. The function isn't very predictable in terms or what you'll get as output. The most reliable way to get timing is to use gettimeofday() which in turn uses a lowlevel clock. I'm not sure exactly what your application is, but sometimes gettimeofday() can be a little complicated to use. Which is why I create the following clocksource changes, ftp://source.mvista.com/pub/dwalker/clocksource/ the purpose of which is to allow generic access to suitable lowlevel clocks. It just extends the mechanism already used by gettimeofday(). Daniel - 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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