linux-kernel - Re: CONFIG_IRQBALANCE for 64-bit x86 ?

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Message-Id: <200711200615.51316.ismail@pardus.org.tr>
Date:	Tue, 20 Nov 2007 06:15:50 +0200
From:	Ismail Dönmez <ismail@...dus.org.tr>
To:	Mark Lord <lkml@....ca>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...l.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: CONFIG_IRQBALANCE for 64-bit x86 ?

Tuesday 20 November 2007 Tarihinde 06:12:21 yazmıştı:
> On 32-bit x86, we have CONFIG_IRQBALANCE available,
> but not on 64-bit x86.  Why not?
>
> I ask, because this feature seems almost essential to obtaining
> reasonable latencies during heavy I/O with fast devices.
>
> My 32-bit Core2Duo MythTV box drops audio frames without it,
> but works perfectly *with* IRQBALANCE.
>
> My QuadCore box works very well in 32-bit mode with IRQBALANCE,
> but responsiveness sucks bigtime when run in 64-bit mode (no IRQBALANCE)
> during periods of multiple heavy I/O streams (USB flash drives).
>
> That's with both the 32 and 64 bit versions of Kubuntu Gutsy,
> so the software uses pretty much identical versions either way.
>
> As near as I can tell, when IRQBALANCE is not configured,
> all I/O device interrupts go to CPU#0.
>
> I don't think our CPU scheduler takes that into account when assigning
> tasks to CPUs, so anything sent to CPU0 runs with very high latencies.
>
> Or something like that.
>
> Why no IRQ_BALANCE in 64-bit mode ?

Have you tried running irqbalance on userspace? Checkout 
http://irqbalance.org/ . AFAIK CONFIG_IRQBALANCE is deprecated and eats 
battery power.

Regards,
ismail

-- 
Faith is believing what you know isn't so -- Mark Twain
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