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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 20 Nov 2007 05:37:42 +0100
From:	Adrian Bunk <bunk@...nel.org>
To:	Willy Tarreau <w@....eu>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, Mark Lord <lkml@....ca>,
	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 ?

On Tue, Nov 20, 2007 at 05:29:29AM +0100, Willy Tarreau wrote:
> On Tue, Nov 20, 2007 at 03:17:15PM +1100, Nick Piggin wrote:
> > On Tuesday 20 November 2007 15:12, Mark Lord wrote:
> > > 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 ?
> > 
> > For that matter, I'd like to know why it has been decided that the
> > best place for IRQ balancing is in userspace. It should be in kernel
> > IMO, and it would probably allow better power saving, performance,
> > fairness, etc. if it were to be integrated with the task balancer as
> > well.
> 
> Agreed. When userspace has something to do with the way IRQs are
> delivered, it's going to smell as bad as micro-kernels...

The next step to a micro-kernel would then be hardware drivers and file 
systems in userspace?  ;-)

> Willy

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/