[PATCH] Fix non-TSC guest clocksource lockup

From: Rusty Russell
Date: Thu Aug 09 2007 - 06:53:21 EST


lguest uses a host-supplied wallclock-based clocksource when the TSC
is not reliable. As this is already in nanoseconds, I naively used a
multiplier of 1 and a shift of 0.

But update_wall_time() in its infinite wisdom decides to adjust the
clock a little (where does it think it's getting a more accurate time
from?)

It will happily tweak the multiplier... to 0, then -1.

So the "fix" is to use a shift of 22 like everyone else, and a
multiplier of 1 << 22.

Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>

diff -r e715c5d0ca6d drivers/lguest/lguest.c
--- a/drivers/lguest/lguest.c Thu Aug 09 15:08:26 2007 +1000
+++ b/drivers/lguest/lguest.c Thu Aug 09 20:42:46 2007 +1000
@@ -691,7 +691,8 @@ static struct clocksource lguest_clock =
.rating = 400,
.read = lguest_clock_read,
.mask = CLOCKSOURCE_MASK(64),
- .mult = 1,
+ .mult = 1 << 22,
+ .shift = 22,
};

/* The "scheduler clock" is just our real clock, adjusted to start at zero */
@@ -774,7 +775,6 @@ static void lguest_time_init(void)
* way, the "rating" is initialized so high that it's always chosen
* over any other clocksource. */
if (lguest_data.tsc_khz) {
- lguest_clock.shift = 22;
lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz,
lguest_clock.shift);
lguest_clock.flags = CLOCK_SOURCE_IS_CONTINUOUS;


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