Re: [PATCH] IPMI: use schedule in kthread

Andrew Morton
2006-06-26T19:01:09Z

On Mon, 26 Jun 2006 09:08:19 -0500
MAILER-DAEMON@osdl.org wrote:

> The kthread used to speed up polling for IPMI was using udelay
> when the lower-level state machine told it to do a short delay.
> This just used CPU and didn't help scheduling, thus causing bad
> problems with other tasks. Call schedule() instead.
>
> Signed-off-by: Corey Minyard <minyard@acm.org>
>
> Index: linux-2.6.17/drivers/char/ipmi/ipmi_si_intf.c
> ===================================================================
> --- linux-2.6.17.orig/drivers/char/ipmi/ipmi_si_intf.c
> +++ linux-2.6.17/drivers/char/ipmi/ipmi_si_intf.c
> @@ -809,7 +809,7 @@ static int ipmi_thread(void *data)
> /* do nothing */
> }
> else if (smi_result == SI_SM_CALL_WITH_DELAY)
> - udelay(1);
> + schedule();
> else
> schedule_timeout_interruptible(1);
> }

calling schedule() isn't a lot of use either.

If CONFIG_PREEMPT it's of no benefit and will just chew CPU.

If !CONFIG_PREEMPT && !need_resched() then it's a no-op and will chew CPU.

If !CONFIG_PREEMPT && need_resched() then yes, it'll schedule away. This
is pretty much the only time that a simple schedule() is useful.

What are we actually trying to do in here?