linux-kernel - Re: x86: Is there still value in having a special tlb flush IPI vector?

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Message-Id: <1217538909.8157.99.camel@twins>
Date:	Thu, 31 Jul 2008 23:15:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Jens Axboe <jens.axboe@...cle.com>, Andi Kleen <ak@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: x86: Is there still value in having a special tlb flush IPI
	vector?

On Thu, 2008-07-31 at 22:57 +0200, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> 
> > Peter Zijlstra wrote:
> > > How about using just arch_send_call_function_single_ipi() to implement
> > > smp_send_reschedule() ?
> > >
> > > The overhead of that is a smp_mb() and a list_empty() check in
> > > generic_smp_call_function_single_interrupt() if there is indeed no work
> > > to do.
> > 
> > Is doing a no-op interrupt sufficient on all architectures?  Is there 
> > some change a function call IPI might not go through the normal 
> > reschedule interrupt exit path?
> 
> We'd still use the smp_send_reschdule(cpu) API, so it's an architecture 
> detail. On x86 we'd use arch_send_call_function_single_ipi().

Also, all interrupts _should_ do the regular interrupt enter/exit paths,
we fixup stuff there, like jiffies and such.

We had a fun NO_HZ bug the other day because some sparc64 IPIs didn't.

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