On Monday 15 October 2007, Anton Blanchard wrote:
> Pull the copy_to_user out of hrtimer_nanosleep and into the callers
> (common_nsleep, sys_nanosleep) in preparation for converting
> compat_sys_nanosleep to use hrtimers.
Looks good, except for two micro-optimization:
> Signed-off-by: Anton Blanchard <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
> @@ -1361,7 +1356,14 @@ sys_nanosleep(struct timespec __user *rqtp, struct timespec __user *rmtp)
> if (!timespec_valid(&tu))
> return -EINVAL;
>
> - return hrtimer_nanosleep(&tu, rmtp, HRTIMER_MODE_REL, CLOCK_MONOTONIC);
> + ret = hrtimer_nanosleep(&tu, &rmt, HRTIMER_MODE_REL, CLOCK_MONOTONIC);
> +
> + if (ret && rmtp) {
> + if (copy_to_user(rmtp, &rmt, sizeof(*rmtp)))
> + return -EFAULT;
> + }
> +
> + return ret;
> }
>
If it's common to call sys_nanosleep with a NULL rmtp argument, we could save a
few cycles using
return hrtimer_nanosleep(&tu, rmtp ? &rmp : NULL, HRTIMER_MODE_REL,
CLOCK_MONOTONIC);
> diff --git a/kernel/posix-timers.c b/kernel/posix-timers.c
> index 57efe04..cce8c75 100644
> --- a/kernel/posix-timers.c
> +++ b/kernel/posix-timers.c
> @@ -980,9 +980,19 @@ sys_clock_getres(const clockid_t which_clock, struct timespec __user *tp)
> static int common_nsleep(const clockid_t which_clock, int flags,
> struct timespec *tsave, struct timespec __user *rmtp)
> {
> - return hrtimer_nanosleep(tsave, rmtp, flags & TIMER_ABSTIME ?
> + struct timespec rmt;
> + int ret;
> +
> + ret = hrtimer_nanosleep(tsave, &rmt, flags & TIMER_ABSTIME ?
> HRTIMER_MODE_ABS : HRTIMER_MODE_REL,
> which_clock);
> +
> + if (ret && rmtp) {
> + if (copy_to_user(rmtp, &rmt, sizeof(*rmtp)))
> + return -EFAULT;
> + }
> +
> + return ret;
> }
I think it would be better here to propagate the move to a kernel *rmtp
down to sys_clock_nanosleep so we get the same optimization in
compat_sys_clock_nanosleep. That should probably also be a separate
patch. I can do one if you don't do it first.
Arnd <><
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