linux-kernel - Re: [RFC PATCH] hrtimer: removing all ur callback modes

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Message-ID: <493E2725.7090305@hartkopp.net>
Date:	Tue, 09 Dec 2008 09:07:01 +0100
From:	Oliver Hartkopp <oliver@...tkopp.net>
To:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH] hrtimer: removing all ur callback modes

Peter Zijlstra wrote:
> On Sun, 2008-12-07 at 13:59 +0100, Oliver Hartkopp wrote:
>   
>> Oliver Hartkopp wrote:
>>     
>>> Peter Zijlstra wrote:
>>>       
>>>> On Tue, 2008-11-25 at 12:43 +0100, Peter Zijlstra wrote:
>>>>  
>>>>         
>>>>> Hi,
>>>>>
>>>>> This is an attempt at removing some of the hrtimer complexity by
>>>>> reducing the number of callback modes to 1.
>>>>>
>>>>> This means that all hrtimer callback functions will be ran from 
>>>>> HARD-irq
>>>>> context.
>>>>>
>>>>>           
>> Hi Peter,
>>
>> i ran a heavy load test, which get's (reproducible) the attached outputs ...
>>
>> Maybe it's not that good to define the hrtimer context to be always 
>> hard-irq.
>>     
>
> Thing is, this 'cleanup' removes quite a bit of complexity from the core
> hrtimer code, and afaict your bit is the only thing that cannot seem to
> cope. So I'd rather look at fixing your site than re-introduce softirqs
> to hrtimers.
>
>   

I wouldn't be that sure that all the other sites can cope with it as i 
only detected the problems with my code under heavy load ...

>> Any idea?
>>     
>
> What are the timing constraints of your problem? - I assume they are not
> too aggressive, otherwise you'd not be able to run from softirq, could
> you run from keventd?
>   

I browsed some code that's using hrtimers and found some hopefully good 
example in drivers/s390/crypto/ap_bus.c : They are using the hrtimer to 
schedule a tasklet which is running in soft-irq context:

http://lxr.linux.no/linux+v2.6.27.8/drivers/s390/crypto/ap_bus.c#L1150

This could also be the correct approach for my sock_queue_rcv_skb() 
problem, right?

Regards,
Oliver

ps. What is the intended release for this hrtimer cleanup? 2.6.29?


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