From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jack Steiner Date: Wed, 04 Feb 2004 19:40:47 +0000 Subject: Re: [PATCH] turn off irqdebug by default on Altix Message-Id: <20040204194047.GC18796@sgi.com> List-Id: References: <20040204152841.GB3387@localhost> In-Reply-To: <20040204152841.GB3387@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org 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). > > mh > > -- > Martin Hicks || mort@bork.org || PGP/GnuPG: 0x4C7F2BEE -- Thanks Jack Steiner (steiner@sgi.com) 651-683-5302 Principal Engineer SGI - Silicon Graphics, Inc.