linux-kernel - Re: Why kmem_cache_free occupy CPU for more than 10 seconds?

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Date:	Fri, 13 Apr 2007 17:26:43 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Zhao Forrest <forrest.zhao@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Why kmem_cache_free occupy CPU for more than 10 seconds?

Zhao Forrest wrote:
> These 2 kernel options are turned on by default in my kernel. Here's
> snip from .config
> # CONFIG_PREEMPT_NONE is not set
> CONFIG_PREEMPT_VOLUNTARY=y
> # CONFIG_PREEMPT is not set
> CONFIG_PREEMPT_BKL=y
> CONFIG_NUMA=y
> CONFIG_K8_NUMA=y
> 
>>
>> Does this fix it?
>>
>> --- fs/buffer.c~        2007-02-01 12:00:34.000000000 +0100
>> +++ fs/buffer.c 2007-04-11 12:35:48.000000000 +0200
>> @@ -3029,6 +3029,8 @@ out:
>>                         struct buffer_head *next = bh->b_this_page;
>>                         free_buffer_head(bh);
>>                         bh = next;
>> +
>> +                       cond_resched();
>>                 } while (bh != buffers_to_free);
>>         }
>>         return ret;
>>
> So far I have run the test with patched kernel for 6 rounds, and
> didn't see the soft lockup. I think this patch should fix the problem.
> But what still confused me is that why do we need to invoke
> cond_resched() voluntarily since CONFIG_PREEMPT_VOLUNTARY and
> CONFIG_PREEMPT_BKL are both turned on? From my understanding these 2
> options should make schedule happen even if CPU is under heavy
> load......

No, only CONFIG_PREEMPT will do that.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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