lkml.org 
[lkml]   [1999]   [Jul]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: PATCH: POSIX 1003.1b timer minor fixes
Robert de Vries wrote:
> Reading the i386 TSC probably takes less time than a system call.

The i386 TSC gives the wrong answers in the presence of APM and
eventually ACPI, due to slowing the clock to save power. I think the
kernel doesn't do any better yet, but with ACPI it has greater control
and so gettimeofday() might just work even with power management.

To argue against myself, it's possible on later x86s to disable
user-space TSC, so it would be possible to trap the rdtsc instruction
when the clock is slowed and substitute a suitably faked up value. That
would only slow the execution path when the clock is slowed for power
management -- at full speed it would be very fast.

To argue conversely again... can you have processors with different
internal clocks (speed & value) in an SMP system?

-- Jamie

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

\
 
 \ /
  Last update: 2005-03-22 13:53    [W:0.053 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site