Date:	Fri, 20 Mar 2009 10:47:01 -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 Fri, Mar 20, 2009 at 10:30:45AM -0500, Corey Minyard wrote:
> Greg KH wrote:
>> 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?
>>   
> It's actually already sort of self-tuning.  kipmid sleeps unless there is 
> IPMI activity.  It only spins if it is expecting something from the 
> controller.
>
> I've been thinking about this a little more.  Assuming that the self-tuning 
> is working (and it appears to be working fine on my systems), that means 
> that something is causing the IPMI driver to constantly talk to the 
> management controller.  I can think of three things:
>
>   1. The user is constantly sending messages to management controller.
>   2. There is something wrong with the hardware, like the ATTN bit is
>      stuck high, causing the driver to constantly poll the management
>      controller.
>   3. The driver either has a bug or needs some more work to account for
>      something the hardware needs it to do to clear the ATTN bit.
>
> If it's #1 above, then I don't know if there is anything we can do about 
> it.  The patch Martin sent will simply slow things down.

Does the "normal" ipmi userspace tools do #1?

For #2, this might make sense, as I have had reports of some hardware
working just fine, while others have the load issue.  Both were
different hardware manufacturers.

> #2 and #3 will require someone to do some debugging.  If the ATTN bit is 
> stuck, you should see the "attentions" field in /proc/ipmi/0/si_stats 
> constantly going up.  Actually, the contents of that file would be helpful, 
> along with /proc/ipmi/0/stats.

Martin has one of these machines, right?  If not, I can dig and try to
get some information as well.

thanks,

greg k-h
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