From: Andi Kleen <ak@suse.de>
To: Ingo Molnar <mingo@elte.hu>
Cc: Andi Kleen <ak@suse.de>,
Ville Herva <vherva@mail.niksula.cs.hut.fi>,
Fabio Riccardi <fabio@chromium.com>,
linux-kernel@vger.kernel.org
Subject: Re: X15 alpha release: as fast as TUX but in user space (fwd)
Date: Sat, 28 Apr 2001 21:53:01 +0200 [thread overview]
Message-ID: <20010428215301.A1052@gruyere.muc.suse.de> (raw)
In-Reply-To: <Pine.LNX.4.33.0104281752290.10866-100000@localhost.localdomain>
In-Reply-To: <Pine.LNX.4.33.0104281752290.10866-100000@localhost.localdomain>; from mingo@elte.hu on Sat, Apr 28, 2001 at 05:52:42PM +0200
On Sat, Apr 28, 2001 at 05:52:42PM +0200, Ingo Molnar wrote:
>
> On Sat, 28 Apr 2001, Andi Kleen wrote:
>
> > You can also just use the cycle counter directly in most modern CPUs.
> > It can be read with a single instruction. In fact modern glibc will do
> > it for you when you use clock_gettime(CLOCK_PROCESS_CPUTIME_ID, ...)
>
> well, it's not reliable while using things like APM, so i'd not recommend
> to depend on it too much.
*If* you use APM on your server boxes. Not likely even when it doesn't have more than one CPU
and it can be checked at runtime.
I guess glibc could also regularly (every 10 calls or so) call regular gettimeofday
to recheck synchronization; at least for a web server that potential inaccuracy would
be acceptable ("best effort") and the cost of the system call is 1/10.
In x86-64 there are special vsyscalls btw to solve this problem that export
a lockless kernel gettimeofday()
-Andi
next prev parent reply other threads:[~2001-04-28 19:53 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-04-28 15:52 Ingo Molnar
2001-04-28 19:53 ` Andi Kleen [this message]
2001-04-28 22:56 ` Richard Gooch
2001-04-29 5:13 ` H. Peter Anvin
2001-04-29 11:14 ` Jeff Garzik
2001-04-29 16:21 ` dean gaudet
2001-04-29 20:19 ` H. Peter Anvin
2001-04-29 21:16 ` Jim Gettys
2001-04-29 21:40 ` H. Peter Anvin
2001-04-29 21:47 ` Jim Gettys
2001-05-02 18:18 ` Matti Aarnio
2001-05-02 19:34 ` Linus Torvalds
2001-05-02 20:55 ` Fabio Riccardi
2001-04-29 22:29 ` Richard Gooch
2001-04-30 7:02 ` David S. Miller
2001-04-30 7:29 ` H. Peter Anvin
2001-04-30 7:51 ` David S. Miller
2001-04-30 14:56 ` Jonathan Lundell
2001-04-29 11:27 ` David S. Miller
2001-04-29 13:32 ` Ingo Oeser
2001-04-29 18:48 ` Richard Gooch
2001-04-29 18:55 ` Gregory Maxwell
2001-04-29 19:02 ` Richard Gooch
2001-04-29 19:47 ` Gregory Maxwell
2001-04-29 19:54 ` Richard Gooch
2001-04-29 20:11 ` Ingo Oeser
2001-04-29 20:18 ` Gregory Maxwell
2001-04-30 0:13 ` Andrea Arcangeli
2001-04-29 20:45 ` Arjan van de Ven
2001-04-29 22:20 ` Richard Gooch
2001-04-30 16:46 ` Alan Cox
2001-04-29 22:18 ` Richard Gooch
2001-04-29 19:38 ` Jamie Lokier
2001-04-29 23:53 ` Andrea Arcangeli
2001-04-30 8:42 ` Pavel Machek
2001-05-03 7:13 ` Kai Henningsen
2001-05-03 7:44 ` Keith Owens
2001-05-03 10:37 ` Ingo Oeser
2001-05-03 15:44 ` Gregory Maxwell
2001-05-07 19:04 ` Pavel Machek
2001-05-03 9:37 ` Alan Cox
2001-05-07 19:03 ` vsyscalls [was Re: X15 alpha release: as fast as TUX but in user space (fwd)] Pavel Machek
2001-05-03 12:23 ` X15 alpha release: as fast as TUX but in user space (fwd) Helge Hafting
2001-05-03 19:09 ` Pavel Machek
2001-05-03 19:50 ` agrawal
2001-05-07 19:07 ` vsyscallRe: " Pavel Machek
2001-05-03 20:19 ` Alan Cox
2001-05-03 20:41 ` Gregory Maxwell
2001-05-04 8:06 ` Pavel Machek
2001-05-04 17:31 ` dean gaudet
2001-05-04 8:43 ` bert hubert
2001-05-02 10:52 ` Andi Kleen
2001-05-02 10:53 ` Ingo Molnar
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