From: Filip Navara <navaraf@reactos.com>
To: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [patch] option -no-tsc for i386 with speedstep
Date: Mon, 25 Apr 2005 22:38:42 +0200 [thread overview]
Message-ID: <426D5552.4000104@reactos.com> (raw)
In-Reply-To: <380218305509284f15ded3ac17915cb1@elis.ugent.be>
Jonas Maebe wrote:
> On 25 Apr 2005, at 22:17, Massimo Dal Zotto wrote:
>
>> In the meantime until we find a better solution could you give us some
>> explanation on why using a microseconds clock from gettimeofday instead
>> of rdtsc the guest os clock runs always 20% slower?
>
> Because a system call (which gettimeofday is) is very slow (two
> context switches).
I remember there was a Linux patch which changed the gettimeofday
function to read the info from user mode shared page (which is updated
by the kernel) and thus avoided the syscall overhead. Not sure if/when
it was integrated into the official sources...
(Once again Windows NT were ahead of time with this idea implemented way
earlier ;-)
- Filip
next prev parent reply other threads:[~2005-04-25 20:50 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-04-25 11:15 [Qemu-devel] [patch] option -no-tsc for i386 with speedstep Massimo Dal Zotto
2005-04-25 15:44 ` [Qemu-devel] " Heike C. Zimmerer
2005-04-25 17:07 ` [Qemu-devel] " Jim C. Brown
2005-04-25 17:28 ` Paul Brook
2005-04-25 17:44 ` Massimo Dal Zotto
2005-04-25 17:47 ` [Qemu-devel] " Heike C. Zimmerer
2005-04-25 18:58 ` [Qemu-devel] " Fabrice Bellard
2005-04-25 20:17 ` Massimo Dal Zotto
2005-04-25 20:24 ` Jonas Maebe
2005-04-25 20:38 ` Filip Navara [this message]
2005-04-25 21:03 ` Lionel Ulmer
2005-04-25 22:45 ` Taras Glek
2005-04-25 21:46 ` [Qemu-devel] [patch] option -no-tsc for i386 with speedstep (solved) Massimo Dal Zotto
2005-04-26 6:50 ` Jonas Maebe
2005-04-26 3:03 ` [Qemu-devel] [patch] option -no-tsc for i386 with speedstep Kyle Hayes
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