linux-kernel - Re: [Discuss] [PATCH] ipmi: use round_jiffies on timers to reduce timer overhead/wakeups

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Date:	Wed, 21 Oct 2009 13:03:48 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	"Kok, Auke" <auke-jan.h.kok@...el.com>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	"discuss@...sWatts.org" <discuss@...sWatts.org>,
	"openipmi-developer@...ts.sourceforge.net" 
	<openipmi-developer@...ts.sourceforge.net>,
	lkml <linux-kernel@...r.kernel.org>,
	Corey Minyard <minyard@....org>
Subject: Re: [Discuss] [PATCH] ipmi: use round_jiffies on timers to reduce
 timer overhead/wakeups

On Wed, 21 Oct 2009 11:49:59 -0700 Kok, Auke wrote:

> Arjan van de Ven wrote:
> > On Wed, 21 Oct 2009 10:28:22 -0700
> > Randy Dunlap <randy.dunlap@...cle.com> wrote:
> > 
> >> From: Randy Dunlap <randy.dunlap@...cle.com>
> >>
> >> Use a round_jiffies() variant to reduce overhead of timer
> >> wakeups.  This causes the ipmi timers to occur at the same
> >> time as other timers (per CPU).
> >>
> >> Typical powertop for /ipmi/ (2.6.31, before patch):
> >>   11.4% (247.4)            kipmi0 : __mod_timer (process_timeout) 
> >>    0.6% ( 13.1)       <interrupt> : ipmi_si 
> >>    0.5% ( 10.0)     <kernel core> : __mod_timer (ipmi_timeout) 
> >>
> >> powertop for /ipmi/, 2.6.31, after patch:
> >>   10.8% (247.6)            kipmi0 : __mod_timer (process_timeout) 
> >>    0.3% (  6.9)       <interrupt> : ipmi_si 
> >>    0.0% (  1.0)     <kernel core> : __mod_timer (ipmi_timeout)
> > 
> > while it is nice that ipmi_si ande the timer wake up less now.... it's
> > still rather sad that the 247.6 from kipmi0 are still there..... those
> > are a much much bigger issue
> 
> obviously :)
> 
> Randy, any idea where those are coming from ?


obviously from kipmi thread :(

drivers/char/ipmi/ipmi_si_intf.c::ipmi_thread():

static int ipmi_thread(void *data)
{
	struct smi_info *smi_info = data;
	unsigned long flags;
	enum si_sm_result smi_result;

	set_user_nice(current, 19);
	while (!kthread_should_stop()) {
		spin_lock_irqsave(&(smi_info->si_lock), flags);
		smi_result = smi_event_handler(smi_info, 0);
		spin_unlock_irqrestore(&(smi_info->si_lock), flags);
		if (smi_result == SI_SM_CALL_WITHOUT_DELAY)
			; /* do nothing */
		else if (smi_result == SI_SM_CALL_WITH_DELAY)
			schedule();
		else
			schedule_timeout_interruptible(1); <-----
	}
	return 0;
}


calls setup_timer_on_stack(), which calls process_timeout().

>From what I recall (probably 2 years ago), [older] ipmi hardware does not
generate event interrupts, so it has to be polled.

Corey, can you elaborate on this?


---
~Randy
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