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Message-Id: <1217602211.4684.9.camel@twins>
Date: Fri, 01 Aug 2008 16:50:11 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Josef Bacik <jbacik@...hat.com>
Cc: Ric Wheeler <rwheeler@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...e.hu>, linux-fsdevel@...r.kernel.org,
Chris Mason <chris.mason@...cle.com>,
linux-kernel@...r.kernel.org
Subject: Re: high resolution timers, scheduling & sleep granularity
On Fri, 2008-08-01 at 09:25 -0400, Josef Bacik wrote:
> Index: linux-2.6/fs/jbd/transaction.c
> ===================================================================
> --- linux-2.6.orig/fs/jbd/transaction.c
> +++ linux-2.6/fs/jbd/transaction.c
> @@ -63,6 +65,32 @@ get_transaction(journal_t *journal, tran
> return transaction;
> }
>
> +static void precision_sleep(unsigned long time)
> +{
> + struct hrtimer_sleeper t;
> +
> + hrtimer_init_on_stack(&t.timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
> + hrtimer_init_sleeper(&t, current);
> + t.timer.expires = ktime_add_ns(ktime_get_real(), time);
> +
> + do {
> + set_current_state(TASK_UNINTERRUPTIBLE);
> +
> + hrtimer_start(&t.timer, t.timer.expires, HRTIMER_MODE_ABS);
> + if (!hrtimer_active(&t.timer))
> + t.task = NULL;
> +
> + if (likely(t.task))
> + schedule();
> +
> + hrtimer_cancel(&t.timer);
> + } while (t.task);
> +
> + set_current_state(TASK_RUNNING);
> +
> + destroy_hrtimer_on_stack(&t.timer);
> +}
> +
> /*
> * Handle management.
> *
I was convinced we already had such a creature,. but I guess I was wrong
as I can't find it ;-)
Anyway, I'm thinking this function ought to live in kernel/hrtimer.c and
possibly get renamed to something like hrtimer_sleep_ns() or some such
(means you can also reuse the do_nanosleep helper in there).
Also, have you considered the impact on platforms that do not support
hrtimers, or don't have high resolution clock events available?
> Index: linux-2.6/kernel/hrtimer.c
> ===================================================================
> --- linux-2.6.orig/kernel/hrtimer.c
> +++ linux-2.6/kernel/hrtimer.c
> @@ -1458,6 +1458,7 @@ void hrtimer_init_sleeper(struct hrtimer
> sl->timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
> #endif
> }
> +EXPORT_SYMBOL_GPL(hrtimer_init_sleeper);
>
> static int __sched do_nanosleep(struct hrtimer_sleeper *t, enum hrtimer_mode mode)
> {
That also gets rid of this export..
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