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Subject: Re: [patch] voluntary-preempt-2.6.8-rc2-L2, preemptable hardirqs
From: Lee Revell <rlrevell@joe-job.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       William Lee Irwin III <wli@holomorphy.com>,
       Lenar L?hmus <lenar@vision.ee>, Andrew Morton <akpm@osdl.org>,
       Arjan van de Ven <arjanv@redhat.com>
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On Wed, 2004-07-28 at 21:08, Lee Revell wrote:
> On Wed, 2004-07-28 at 17:50, Lee Revell wrote:
> > On Wed, 2004-07-28 at 01:05, Ingo Molnar wrote:
> > > * Lee Revell <rlrevell@joe-job.com> wrote:
> > > if your soundcard doesnt share the irq line with any other 'heavy' 
> > > interrupt then you can make the irq 'direct' via a simple change to 
> > > arch/i386/kernel/irq.c, change this line from:
> > > 
> > >  #define redirectable_irq(irq) ((irq) != 0)
> > > 
> > > to:
> > > 
> > >  #define redirectable_irq(irq) (((irq) != 0) && ((irq) != 10))
> > > 
> > > (if the soundcard is on IRQ 10).
> > > 
> > > does such a change combined with v=3 fix the latencies you are seeing?
> > 
> > With L2, 1:3, max_sectors_kb=256, and the above change, the performance
> > is truly amazing.  Over 20 million interrupts, on a 600Mhz machine, the
> > worst latency I was able to trigger was 46 usecs.  There does not seem
> > to be any adverse affect on any aspect of the system.
> > 
> 
> Here are some more results.  I am up to 56 million interrupts and I have
> yet to trigger a latency higher than 46 usecs.  It looks like this is a
> hard upper limit.

I have also found that if I stress the VM subsystem severely using
sysbench --threads=128 --test=memory, jackd will not start, eventually
its watchdog thread will kill it before it opens the audio ports.  It
seems likely that under pressure the mlockall() would never return.  I
can add some debugging code to jackd if you need to see which system
call is timing out.

Lee