Re: [PATCH] turn off irqdebug by default on Altix

From: Martin Hicks <mort_at_sgi.com>
Date: 2004-02-06 05:37:28
On Wed, Feb 04, 2004 at 01:40:47PM -0600, Jack Steiner wrote:
> On Wed, Feb 04, 2004 at 02:08:05PM -0500, Martin Hicks wrote:
> > 
> > 
> > On Wed, Feb 04, 2004 at 11:04:43AM -0800, Chen, Kenneth W wrote:
> > > This is really confusing with two parameters that do the same thing.
> > > What will happen if someone pass noirqdebug and irqdebug at the same
> > > time?
> > > 
> > > What's wrong with boot time parameter of noirqdebug?
> > 
> > It just means that if you forget to pass this option then your machine
> > never boots.  Well, it will boot.  Eventually.  Jack is a patient man,
> > and he said he never waited long enough for it to boot.
> 
> Actually, I determined that a big system would never boot. Each cpu would have to
> do about 1500usec of work every 1000usec.  (highly dependent on the
> system interconnect).
> 
> Each clock tick, the desc->irq_count is incremented by each cpu. On a big
> system, this creates an incredibly hot cache line. On a big system, it takes
> more than a millisecond to do the update. At that point, another clock
> interrupt is already pending. Forward progress stops.
> 
> Another possible approach might be to special case note_interrupt() to
> skip the update for the timer tick. (I havent actually looked at the code, but
> this should be possible). 

Okay.  This is certainly less messy, and is IA64 specific.

How about this patch?  I just tested it on a 512p machine and it booted.

mh

-- 
Martin Hicks   ||   Silicon Graphics Inc.   ||   mort@sgi.com

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Received on Thu Feb 5 13:41:21 2004

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