linux-kernel - Re: [PATCH] Re: Bad network performance over 2Gbps

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Date:	Mon, 21 Apr 2008 09:38:49 -0700
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Pavel Machek <pavel@....cz>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Anton Titov <a.titov@...t.bg>, Chris Snook <csnook@...hat.com>,
	"H. Willstrand" <h.willstrand@...il.com>, netdev@...r.kernel.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Re: Bad network performance over 2Gbps

Pavel Machek wrote:
> Hi!
> 
>> [X86] IRQBALANCE: Mark as BROKEN and disable by default
>>
>> The IRQBALANCE option causes interrupts to bounce all around on SMP systems
>> quickly burying the CPU in migration cost and cache misses. Mainly affected are
>> network interrupts and this results in one CPU pegged in softirqd completely.
>>
>> Disable this option and provide documentation to a better solution (userspace
>> irqbalance daemon does overall the best job to begin with and only manual setting
>> of smp_affinity will beat it).
>>
>> Signed-off-by: Auke Kok <auke-jan.h.kok@...el.com>
>>
>> ---
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 6c70fed..956aa22 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1026,13 +1026,17 @@ config EFI
>>    	platforms.
>>
>>  config IRQBALANCE
>> -	def_bool y
>> +	def_bool n
> 
> ACK.
>>  	prompt "Enable kernel irq balancing"
>> -	depends on X86_32 && SMP && X86_IO_APIC
>> +	depends on X86_32 && SMP && X86_IO_APIC && BROKEN
> 
> This is wrong. irqbalance works, there's nothing wrong with it; but it
> has nasty sideffects.

ok, I'm fine with taking that part out of the patch.

Ingo, want me to send an updated patch?


> 
>>  	help
>>  	  The default yes will allow the kernel to do irq load balancing.
>>  	  Saying no will keep the kernel from doing irq load balancing.
>>
>> +	  This option is known to cause performance issues on SMP
>> +	  systems. The preferred method is to use the userspace
>> +	  'irqbalance' daemon instead. See http://irqbalance.org/.
>> +
> 
> ACK.
> 

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