From: "David S. Miller" <davem@redhat.com>
To: jamesclv@us.ibm.com
Cc: ak@suse.de, alan@lxorguk.ukuu.org.uk,
linux-kernel@vger.kernel.org, johnstul@us.ibm.com,
anton.wilson@camotion.com
Subject: Re: do_gettimeofday vs. rdtsc in the scheduler
Date: Tue, 17 Sep 2002 16:12:15 -0700 (PDT) [thread overview]
Message-ID: <20020917.161215.03597459.davem@redhat.com> (raw)
In-Reply-To: <200209171555.52872.jamesclv@us.ibm.com>
From: James Cleverdon <jamesclv@us.ibm.com>
Date: Tue, 17 Sep 2002 15:55:52 -0700
The initial sync was easy, even with variable latencies on cache lines. A
much simplified NTP-ish algorithm works fine. The painful thing was bus
clock drift and programs that foolishly relied on the TSC being the same
between CPUs and between nodes.
This is why the gettimeofday implementation should use the system tick
thing and also any profiling support in the C library should avoid
TSC as well.
For small stretches of code TSC can be used for very precise profiling
but otherwise it is pretty useless by in large.
next prev parent reply other threads:[~2002-09-17 23:16 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <200209172020.g8HKKPF13227@eng2.beaverton.ibm.com.suse.lists.linux.kernel>
[not found] ` <1032294559.22815.180.camel@cog.suse.lists.linux.kernel>
[not found] ` <20020917.133933.69057655.davem@redhat.com.suse.lists.linux.kernel>
2002-09-17 21:00 ` do_gettimeofday vs. rdtsc in the scheduler Andi Kleen
2002-09-17 20:54 ` David S. Miller
2002-09-17 21:28 ` Alan Cox
2002-09-17 21:18 ` David S. Miller
2002-09-17 22:02 ` James Cleverdon
2002-09-17 22:44 ` Andi Kleen
2002-09-17 22:38 ` David S. Miller
2002-09-17 22:55 ` James Cleverdon
2002-09-17 23:12 ` David S. Miller [this message]
2002-09-17 23:32 ` john stultz
2002-09-17 23:32 ` David S. Miller
2002-09-17 23:52 ` Andi Kleen
2002-09-17 23:46 ` David S. Miller
2002-09-17 23:58 ` Andi Kleen
2002-09-17 23:51 ` David S. Miller
2002-09-18 0:05 ` Andi Kleen
2002-09-18 1:04 ` James Cleverdon
2002-09-19 18:02 ` Andrea Arcangeli
2002-09-20 11:04 ` Maciej W. Rozycki
2002-09-19 11:20 ` Mikael Pettersson
2002-09-19 13:27 ` Alan Cox
2002-09-19 13:39 ` Mikael Pettersson
2002-09-20 15:26 ` John Levon
2002-09-18 6:40 ` Vojtech Pavlik
2002-09-19 18:04 ` Andrea Arcangeli
[not found] <200209172020.g8HKKPF13227@eng2.beaverton.ibm.com>
2002-09-17 20:29 ` Fwd: " john stultz
2002-09-17 20:39 ` David S. Miller
2002-09-17 20:57 ` john stultz
2002-09-17 20:56 ` David S. Miller
2002-09-09 22:21 anton wilson
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