From: Ravikiran G Thirumalai <kiran@in.ibm.com>
To: Jack Steiner <steiner@sgi.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: hot cache line due to note_interrupt()
Date: Tue, 11 Nov 2003 13:59:15 +0530 [thread overview]
Message-ID: <20031111082915.GC1130@llm08.in.ibm.com> (raw)
In-Reply-To: <20031110215844.GC21632@sgi.com>
On Mon, Nov 10, 2003 at 03:58:44PM -0600, Jack Steiner wrote:
>
> I dont know the background on note_interrupt() in arch/ia64/kernel/irq.c,
> but I had to disable the function on our large systems (IA64).
>
> The function updates a counter in the irq_desc_t table. An entry in this table
> is shared by all cpus that take a specific interrupt #. For most interrupt #'s,
> this is a problem but it is prohibitive for the timer tick on big systems.
>
> Updating the counter causes a cache line to be bounced between
> cpus at a rate of at least HZ*active_cpus. (The number of bus transactions
The answer to this is probably alloc_percpu for the counters.
right now this might not possible because irq_desc_t table might be used very
early, and alloc_percpu uses slab underneath. alloc_percpu will have to be
made to work early enough for this....
Thanks,
Kiran
next prev parent reply other threads:[~2003-11-11 8:23 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-11-10 21:58 hot cache line due to note_interrupt() Jack Steiner
2003-11-10 23:00 ` Anton Blanchard
2003-11-11 8:29 ` Ravikiran G Thirumalai [this message]
2003-11-11 16:25 ` Anton Blanchard
2003-11-11 19:58 ` Andrew Morton
2003-11-14 17:45 ` Jack Steiner
2003-11-14 17:57 ` Andrew Morton
2003-11-14 18:11 ` Jack Steiner
2003-11-14 18:10 ` David Mosberger
2003-11-14 18:17 ` Linus Torvalds
2003-11-15 5:18 ` Jeff Garzik
2003-11-14 19:10 ` Anton Blanchard
2003-11-14 19:28 ` Mike Fedyk
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