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

From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
	Nick Piggin <nickpiggin@yahoo.com.au>,
	Jens Axboe <jens.axboe@oracle.com>, Andi Kleen <ak@suse.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: x86: Is there still value in having a special tlb flush IPI vector?
Date: Thu, 31 Jul 2008 23:15:09 +0200	[thread overview]
Message-ID: <1217538909.8157.99.camel@twins> (raw)
In-Reply-To: <20080731205726.GE25138@elte.hu>

On Thu, 2008-07-31 at 22:57 +0200, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@goop.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.