lkml.org 
[lkml]   [2003]   [Oct]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: gettimeofday resolution seriously degraded in test9
>>>>> "Richard" == Richard B Johnson <root@chaos.analogic.com> writes:

Richard> There isn't any magic that can solve this problem. It turns
Richard> out that with later Intel CPUs, one can get CPU-clock
Richard> resolution from rdtsc. However, this is hardware-specific. If
Richard> somebody modifies the gettimeofday() and the POSIX clock
Richard> routines to use rdtsc when available, a lot of problems will
Richard> go away.

gettimofday() and the posix clock routines (which use gettimeofday())
*do* use rdtsc if the processor has a reliable one --- do_gettimeofday() calls
cur_timer->get_offset(), which is essentially a scaled rdtsc if you're
using timers_tsc.c.

But when you have power management turned on, TSC doesn't run at a
constant rate. If it gets *too* slow, the timer switches to use the
PIT instead, and one loses the cycle-resolution one would otherwise have.

--
Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au
You are lost in a maze of BitKeeper repositories, all slightly different.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:58    [from the cache]
©2003-2011 Jasper Spaans