Messages in this thread Patch in this message | | | Date | Mon, 17 Mar 2008 13:03:28 -0400 | From | Jeff Dike <> | Subject | Re: [2.6.24.x] UML select()/poll() oversleeping reproducibly (was Re: [uml-devel] g_timeout_add) |
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On Fri, Mar 14, 2008 at 11:01:35PM +0000, Nix wrote: > bash-3.2# ./select-sleep 10 > Slept for 13 seconds.
See what kind of difference the patch below makes - it reduces the 30% oversleeping down to 10% for me. That's still way too much, but it's better.
The problem being fixed here is that setitimer consistently returns a remaining time greater than what was originally requested, by ~20%:
1205773032.413780 setitimer(ITIMER_VIRTUAL, {it_interval={0, 10000}, it_value={0, 10000}}, NULL) = 0 1205773032.413814 setitimer(ITIMER_VIRTUAL, {it_interval={0, 0}, it_value={0, 0}}, {it_interval={0, 10998}, it_value={0, 11998}}) = 0
This is setting a 100 HZ timer, immediately followed by a cancellation which also requests the amount left on the timer. The interval is rounded up by 10%, and the first tick by 20%.
Jeff
-- Work email - jdike at linux dot intel dot com
Index: linux-2.6.22/arch/um/os-Linux/time.c =================================================================== --- linux-2.6.22.orig/arch/um/os-Linux/time.c 2008-02-18 11:53:51.000000000 -0500 +++ linux-2.6.22/arch/um/os-Linux/time.c 2008-03-17 12:55:41.000000000 -0400 @@ -58,12 +58,17 @@ static inline long long timeval_to_ns(co long long disable_timer(void) { struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } }); + int remain, max = UM_NSEC_PER_SEC / UM_HZ; if (setitimer(ITIMER_VIRTUAL, &time, &time) < 0) printk(UM_KERN_ERR "disable_timer - setitimer failed, " "errno = %d\n", errno); - return timeval_to_ns(&time.it_value); + remain = timeval_to_ns(&time.it_value); + if (remain > max) + remain = max; + + return remain; } long long os_nsecs(void)
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