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Commit b2468e52 authored by Jan Beulich's avatar Jan Beulich Committed by Linus Torvalds
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[PATCH] x86_64: fix last_tsc calculation of PM timer 



From: "Jan Beulich" <jbeulich@novell.com>

The PM timer code updates vxtime.last_tsc, but this update was done
incorrectly in two ways:
- offset_delay being in microseconds requires multiplying with cpu_mhz
  rather than cpu_khz
- the multiplication of offset_delay and cpu_khz (both being 32-bit
  values) on most current CPUs would overflow (observed value of the
  delay was approximately 4000us, yielding an overflow for frequencies
  starting a little above 1GHz)

Signed-off-by: default avatarJan Beulich <jbeulich@novell.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 2ba567cb

arch/x86_64/kernel/pmtimer.c

+1 −1
Original line number Diff line number Diff line
@@ -68,7 +68,7 @@ int pmtimer_mark_offset(void) 
	offset_delay = delta % (USEC_PER_SEC / HZ);



	rdtscll(tsc);

	vxtime.last_tsc = tsc - offset_delay * cpu_khz;

	vxtime.last_tsc = tsc - offset_delay * (u64)cpu_khz / 1000;



	/* don't calculate delay for first run,

	   or if we've got less then a tick */