linux-kernel - Re: [Openipmi-developer] Improving IPMI performance under load

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Date:	Tue, 24 Mar 2009 08:08:36 -0500
From:	Corey Minyard <minyard@....org>
To:	Martin Wilck <martin.wilck@...itsu-siemens.com>
Cc:	Greg KH <greg@...ah.com>,
	"openipmi-developer@...ts.sourceforge.net" 
	<openipmi-developer@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Openipmi-developer] Improving IPMI performance under load

Martin Wilck wrote:
> Hi Corey,
>
> yesterday I posted some results about the IPMI performance under CPU 
> load, which can be up to 25 times slower than in an idle system. I think 
> it might be worthwhile to try to improve that behavior as well.
>   
Yes, that would be expected, as kipmid would never be scheduled in a 
busy system, and it would just be the timer driving things.

> I made a variation of my patch which introduces a second parameter 
> (kipmid_min_busy) that causes kipmid not to call schedule() for a 
> certain amount of time. Thus if there's IPMI traffic pending, kipmid 
> will busy-loop for kipmid_min_busy seconds, then starting to schedule() 
> in each loop as it does now, and finally go to sleep when 
> kipmid_max_busy is reached. At the same time, I changed the nice value 
> of kipmid from 19 to 0.
>   
I would guess that changing the nice value is the main thing that caused 
the difference.  The other changes probably didn't make as big a difference.

> With this patch and e.g. min_busy=100 and max_busy=200, there is no 
> noticeable difference any more between IPMI performance with and without 
> CPU load.
>
> The patch + results still need cleanup, therefore I am not sending it 
> right now. Just wanted to hear what you think.
>   
I'm ok with tuning like this, but most users are probably not going to 
want this type of behavior.

-corey
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