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Message-ID: <20080907111137.76a10b1e@infradead.org>
Date: Sun, 7 Sep 2008 11:11:37 -0700
From: Arjan van de Ven <arjan@...radead.org>
To: linux-kernel@...r.kernel.org
Cc: mingo@...e.hu, tglx@...x.de, torvalds@...ux-foundation.org,
peterz@...radead.org
Subject: update on hrtimer based select/poll and range-hrtimers
Hi,
since the last lkml posting I've merged a few fixes and added comments
from Peter, and I've redone the "estimate_accuracy" function.
Rather than reposting the entire series, I'll point to the git tree at
git://git.kernel.org/pub/scm/linux/kernel/git/arjan/linux-2.6-hrtimer.git
and I've pasted the new function below.
Rather than having the hardcoded steps from the "Linus" function, I've
turned it into:
0 for realtime tasks
"0.1% of the time" for not-nice, not realtime tasks
"0.5% of the time" for nice, not realtime tasks
with a cap of 100msec for both.
I would like to request feedback on this approach; I think this is
better than the "hardcoded steps" as before, but maybe someone can come
up with an ever better idea....
static unsigned long __estimate_accuracy(struct timespec *tv)
{
unsigned long slack;
int divfactor = 1000;
if (task_nice(current))
divfactor = divfactor / 5;
slack = tv->tv_nsec / divfactor;
slack += tv->tv_sec * (NSEC_PER_SEC/divfactor);
if (slack > 100 * NSEC_PER_MSEC)
slack = 100 * NSEC_PER_MSEC;
return slack;
}
static unsigned long estimate_accuracy(struct timespec *tv)
{
unsigned long ret;
struct timespec now;
/*
* Realtime tasks get a slack of 0 for obvious reasons.
*/
if (current->policy == SCHED_FIFO ||
current->policy == SCHED_RR)
return 0;
ktime_get_ts(&now);
now = timespec_sub(*tv, now);
ret = __estimate_accuracy(&now);
if (ret < current->timer_slack_ns)
return current->timer_slack_ns;
return ret;
}
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