On Sat, Apr 05, 2008 at 05:45:39PM +0100, Nix wrote:
> The fixed timer patch you posted a few weeks back has indeed fixed my
> select()-based timeout woes.
>
> Unfortunately, both with the old kludgy approach and with the new
> remain-versus-max estimator code, I see intermittent tight lockups of
> the UML kernel-space ptrace thread, with that thread chewing all
> available CPU time and the virtual machine, unsurprisingly, going
> unresponsive.
Below is another patch for you to try. I spent most of last week
chasing this one. The symptoms are somewhat similar to yours -
intermittent UML hangs, although not with UML spinning, and it still
pings.
The problem is NTP adjusting the multiplier part of the clock-provided
cycles-to-ns conversion function. UML pretended to have a ns clock,
with a multiplier of 1. When NTP adjusted that down in order to slow
down the clock, that became 0, and time stopped.
The fix below is to switch to a usec clock, with a multiplier of 1000,
which can be adjusted with much more granualarity.
Jeff
--
Work email - jdike at linux dot intel dot com
Index: linux-2.6.22/arch/um/kernel/time.c
===================================================================
--- linux-2.6.22.orig/arch/um/kernel/time.c 2008-04-10 12:53:32.000000000
-0400
+++ linux-2.6.22/arch/um/kernel/time.c 2008-04-14 10:30:00.000000000 -0400
@@ -75,7 +75,7 @@ static irqreturn_t um_timer(int irq, voi
static cycle_t itimer_read(void)
{
- return os_nsecs();
+ return os_nsecs() / 1000;
}
static struct clocksource itimer_clocksource = {
@@ -83,7 +83,7 @@ static struct clocksource itimer_clockso
.rating = 300,
.read = itimer_read,
.mask = CLOCKSOURCE_MASK(64),
- .mult = 1,
+ .mult = 1000,
.shift = 0,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
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