linux-kernel - Re: [PATCH] limit CPU time spent in kipmid

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Date:	Thu, 19 Mar 2009 16:51:14 -0700
From:	Greg KH <greg@...ah.com>
To:	Corey Minyard <minyard@....org>
Cc:	Martin Wilck <martin.wilck@...itsu-siemens.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	openipmi-developer@...ts.sourceforge.net
Subject: Re: [PATCH] limit CPU time spent in kipmid

On Thu, Mar 19, 2009 at 04:31:00PM -0500, Corey Minyard wrote:
> Martin, thanks for the patch.  I had actually implemented something like 
> this before, and it didn't really help very much with the hardware I had, 
> so I had abandoned this method.  There's even a comment about it in 
> si_sm_result smi_event_handler(). Maybe making it tunable is better, I 
> don't know.  But I'm afraid this will kill performance on a lot of systems.
>
> Did you test throughput on this?  The main problem people had without 
> kipmid was that things like firmware upgrades took a *long* time; adding 
> kipmid improved speeds by an order of magnitude or more.
>
> It's my opinion that if you want this interface to work efficiently with 
> good performance, you should design the hardware to be used efficiently by 
> using interrupts (which are supported and disable kipmid).  With the way 
> the hardware is defined, you cannot have both good performance and low CPU 
> usage without interrupts.
>
> It may be possible to add an option to choose between performance and 
> efficiency, but it will have to default to performance.

I would think that very infrequent things, like firmware upgrades, would
not take priority over a long-term "keep the cpu busy" type system, like
what we currently have.

Is there any way to switch between the different modes dynamically?

I like the idea of this change, as I have got a lot of complaints lately
about kipmi taking way too much cpu time up on idle systems, messing up
some user's process accounting rules in their management systems.  But I
worry about making it a module parameter, why can't this be a
"self-tunable" thing?

thanks,

greg k-h
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