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SubjectRe: [PATCH 13/13] hrtimer: make select() and poll() use the hrtimer range feature
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On Mon, 2008-09-01 at 16:14 -0700, Arjan van de Ven wrote:
> From: Arjan van de Ven <arjan@linux.intel.com>
> Subject: [PATCH] hrtimer: make select() and poll() use the hrtimer range feature
>
> This patch makes the select() and poll() hrtimers use the new range
> feature and settings from the task struct.
>
> In addition, this includes the estimate_accuracy() function that Linus
> posted to lkml (but with a few steps added based on experiments).
>
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
> ---
> fs/select.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 files changed, 66 insertions(+), 2 deletions(-)
>
> diff --git a/fs/select.c b/fs/select.c
> index f6dceb5..21bf77d 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -28,6 +28,62 @@
>
> #include <asm/uaccess.h>
>
> +
> +/* Estimate expected accuracy in ns from a timeval */
> +
> +static unsigned long __estimate_accuracy(struct timespec *tv)
> +{
> + /*
> + * Tens of ms if we're looking at seconds, even
> + * more for 10s+ sleeping
> + */
> + if (tv->tv_sec) {
> + /* 100 milliseconds for long sleeps */
> + if (tv->tv_sec > 10)
> + return 100 * NSEC_PER_MSEC;
> +
> + /*
> + * Tens of ms for second-granularity sleeps. This,
> + * btw, is the historical Linux 100Hz timer range.
> + */
> + return 10 * NSEC_PER_MSEC;
> + }
> +
> + /* 5 msec if we're looking at 100+ milliseconds */
> + if (tv->tv_nsec > 100 * NSEC_PER_MSEC)
> + return 5 * NSEC_PER_MSEC;
> +
> + /* A msec if we're looking at 10+ milliseconds */
> + if (tv->tv_nsec > 10 * NSEC_PER_MSEC)
> + return NSEC_PER_MSEC;
> +
> + /* half a msec if we're looking at milliseconds */
> + if (tv->tv_nsec > NSEC_PER_MSEC)
> + return NSEC_PER_MSEC/2;
> +
> + /* Single usecs if we're looking at microseconds */
> + if (tv->tv_nsec > NSEC_PER_USEC)
> + return NSEC_PER_USEC;
> +
> + /* Aim for tenths of nanosecs otherwise */
> + return 10;
> +}

Why not use a simple logarithmic decay to drive this estimate?




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