From: george anzinger <george@mvista.com>
To: Martin Waitz <tali@admingilde.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Clock monotonic a suggestion
Date: Fri, 21 Mar 2003 11:18:55 -0800 [thread overview]
Message-ID: <3E7B659F.9020407@mvista.com> (raw)
In-Reply-To: <20030321131744.GL27366@admingilde.org>
Martin Waitz wrote:
> On Thu, Mar 20, 2003 at 04:16:13PM -0800, george anzinger wrote:
>
>>Define CLOCK_MONOTONIC to be the same as
>>(gettimeofday() + wall_to_monotonic).
>
>
> why don't you simply use asm("rdtsc") ?
> (ok, you should make sure that you always ask the same processor and
> stuff, but using the built in TSC seems to do everything you want...)
>
>
I don't really understand how :(
I want a tick on CLOCK_MONOTONIC to be the same size as a tick on
gettimeofday() over the life of the system. I.e. lock step. The only
difference is that CLOCK_MONOTONIC can not be set, so, if we use the
above, wall_to_monotonic must be adjusted when the gettimeofday()
clock is set (but not when it is "adjusted" by NTP).
asm("rdtsc") is, first of all, only useful on x86 platforms,
CLOCK_MONOTONIC is in the POSIX clocks and timers code and in all
platforms. Second, each platform has an equivalent, best guess, way
of filling in the time information below the 1/HZ level (and yes, some
x86 platforms use TSC) already in the gettimeofday() code. Except
that the system settime code is platform dependent, this solution is
platform independent.
--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml
next prev parent reply other threads:[~2003-03-21 19:09 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-03-21 0:16 Clock monotonic a suggestion george anzinger
2003-03-21 2:50 ` Joel Becker
2003-03-21 5:53 ` Chris Friesen
2003-03-21 8:10 ` george anzinger
2003-03-21 8:01 ` george anzinger
2003-03-21 19:43 ` Joel Becker
2003-03-21 20:53 ` john stultz
2003-03-21 13:17 ` Martin Waitz
2003-03-21 19:18 ` george anzinger [this message]
2003-03-21 19:46 ` Joel Becker
2003-03-21 19:44 ` Joel Becker
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