netdev - Re: 2.6.24 BUG: soft lockup

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Date:	Thu, 27 Mar 2008 18:58:18 -0700
From:	Matheos Worku <Matheos.Worku@....COM>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>, jesse.brandeburg@...el.com,
	jarkao2@...il.com, netdev@...r.kernel.org, hadi@...erus.ca
Subject: Re: 2.6.24 BUG: soft lockup - CPU#X

Herbert Xu wrote:
> On Thu, Mar 27, 2008 at 05:34:18PM -0700, David Miller wrote:
>   
>> The first cpu will get into __qdisc_run(), but the other
>> ones will just q->enqueue() and exit since the first cpu
>> has indicated it is processing the qdisc.
>>     
>
> Indeed.  Since I created the problem it's only fair that I get
> to fix it too :)
>
> [NET]: Add preemption point in qdisc_run
>
> The qdisc_run loop is currently unbounded and runs entirely
> in a softirq.  This is bad as it may create an unbounded softirq
> run.
>
> This patch fixes this by calling need_resched and breaking out
> if necessary.
>
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
>
> Thanks,
>   
Great.

In general, while the TX serialization  improves performance in terms to 
lock contention, wouldn't it reduce throughput since only one guy is 
doing the actual TX at any given time.  Wondering if it would be 
worthwhile to have an  enable/disable option specially for multi queue TX.

Regards
Matheos

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