On Tue, 27 Nov 2007 15:03:47 -0500
Jeff Dike <[email protected]> wrote:
> [ This one needs to get into 2.6.24 ]
>
> With NO_HZ disabled, the UML idle loop effectively becomes a busy
> loop, as it will sleep for no time.
>
> The cause was forgetting to restart the tick after waking up from
> sleep. It was disabled before sleeping, and the remaining time used
> as the interval to sleep. So, the tick needs to be restarted when
> nanosleep finishes.
>
> This is done by introducing after_sleep_interval, which is empty in
> the NO_HZ case, but which sets the tick starting in the !NO_HZ case.
>
> Signed-off-by: Jeff Dike <[email protected]>
> ---
> arch/um/os-Linux/time.c | 54 +++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 51 insertions(+), 3 deletions(-)
>
> Index: linux-2.6.22/arch/um/os-Linux/time.c
> ===================================================================
> --- linux-2.6.22.orig/arch/um/os-Linux/time.c 2007-11-14 10:33:29.000000000 -0500
> +++ linux-2.6.22/arch/um/os-Linux/time.c 2007-11-26 15:50:46.000000000 -0500
> @@ -59,7 +59,7 @@ long long disable_timer(void)
> {
> struct itimerval time = ((struct itimerval) { { 0, 0 }, { 0, 0 } });
>
> - if(setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
> + if (setitimer(ITIMER_VIRTUAL, &time, &time) < 0)
> printk(UM_KERN_ERR "disable_timer - setitimer failed, "
> "errno = %d\n", errno);
>
> @@ -74,13 +74,61 @@ long long os_nsecs(void)
> return timeval_to_ns(&tv);
> }
>
> +#ifdef UML_CONFIG_NO_HZ
Nothing ever defines this?
> +static int after_sleep_interval(struct timespec *ts)
> +{
> +}
> +#else
> +static inline long long timespec_to_us(const struct timespec *ts)
> +{
> + return ((long long) ts->tv_sec * UM_USEC_PER_SEC) +
> + ts->tv_nsec / UM_NSEC_PER_USEC;
> +}
> +
> +static int after_sleep_interval(struct timespec *ts)
> +{
> + int usec = UM_USEC_PER_SEC / UM_HZ;
> + long long start_usecs = timespec_to_us(ts);
> + struct timeval tv;
> + struct itimerval interval;
> +
> + /*
> + * It seems that rounding can increase the value returned from
> + * setitimer to larger than the one passed in. Over time,
> + * this will cause the remaining time to be greater than the
> + * tick interval. If this happens, then just reduce the first
> + * tick to the interval value.
> + */
> + if (start_usecs > usec)
> + start_usecs = usec;
> + tv = ((struct timeval) { .tv_sec = start_usecs / UM_USEC_PER_SEC,
> + .tv_usec = start_usecs % UM_USEC_PER_SEC });
> + interval = ((struct itimerval) { { 0, usec }, tv });
> +
> + if (setitimer(ITIMER_VIRTUAL, &interval, NULL) == -1)
> + return -errno;
> +
> + return 0;
> +}
> +#endif
> +
> extern void alarm_handler(int sig, struct sigcontext *sc);
>
> void idle_sleep(unsigned long long nsecs)
> {
> - struct timespec ts = { .tv_sec = nsecs / UM_NSEC_PER_SEC,
> - .tv_nsec = nsecs % UM_NSEC_PER_SEC };
> + struct timespec ts;
> +
> + /*
> + * nsecs can come in as zero, in which case, this starts a
> + * busy loop. To prevent this, reset nsecs to the tick
> + * interval if it is zero.
> + */
> + if (nsecs == 0)
> + nsecs = UM_NSEC_PER_SEC / UM_HZ;
> + ts = ((struct timespec) { .tv_sec = nsecs / UM_NSEC_PER_SEC,
> + .tv_nsec = nsecs % UM_NSEC_PER_SEC });
>
> if (nanosleep(&ts, &ts) == 0)
> alarm_handler(SIGVTALRM, NULL);
> + after_sleep_interval(&ts);
> }
-
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