From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759036AbaELRRm (ORCPT ); Mon, 12 May 2014 13:17:42 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:49454 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752383AbaELRRl convert rfc822-to-8bit (ORCPT ); Mon, 12 May 2014 13:17:41 -0400 Date: Mon, 12 May 2014 19:17:29 +0200 From: Peter Zijlstra To: Frederic Weisbecker Cc: LKML , Andrew Morton , Benjamin Herrenschmidt , "David S. Miller" , Ingo Molnar , Kevin Hilman , "Paul E. McKenney" , Paul Mackerras , Russell King , Thomas Gleixner , Viresh Kumar Subject: Re: [PATCH 1/5] irq_work: Architecture support for remote irq work raise Message-ID: <20140512171729.GD13467@laptop.programming.kicks-ass.net> References: <1399851237-2226-1-git-send-email-fweisbec@gmail.com> <1399851237-2226-2-git-send-email-fweisbec@gmail.com> <20140512075650.GJ30445@twins.programming.kicks-ass.net> <20140512162641.GA28033@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: <20140512162641.GA28033@localhost.localdomain> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 12, 2014 at 06:26:49PM +0200, Frederic Weisbecker wrote: > On Mon, May 12, 2014 at 09:56:50AM +0200, Peter Zijlstra wrote: > > On Mon, May 12, 2014 at 01:33:53AM +0200, Frederic Weisbecker wrote: > > > We are going to extend irq work to support remote queuing. > > > > > > So lets add a cpu argument to arch_irq_work_raise(). The architectures > > > willing to support that must then provide the backend to raise irq work > > > IPIs remotely. > > > > > > Initial support is provided for x86 and ARM since they are easily > > > extended. The other archs that overwrite arch_irq_work_raise() seem > > > to use local clock interrupts and therefore need deeper rewrite of their > > > irq work support to implement remote raising. > > > > > > > > Signed-off-by: Frederic Weisbecker > > > > Why not borrow the smp_call_function IPI for the remote bits? We could > > limit the 'safe from NMI' to the local works. And we validate this by > > putting a WARN_ON(in_nmi()) in irq_work_queue_on(). > > Right, but although I don't need it to be safe from NMI, I need it > to be callable concurrently and when irqs are disabled. > > So we can't use smp_call_function_single() for that. But we can use the async > version in which case we must keep the irq work claim. But that's > about the same than smp_queue_function_single() we had previously > and we are back with our csd_lock issue. Who said anything about using smp_call_function_single()? --- diff --git a/kernel/irq_work.c b/kernel/irq_work.c index a82170e2fa78..2fc9d8ece05a 100644 --- a/kernel/irq_work.c +++ b/kernel/irq_work.c @@ -61,7 +61,8 @@ void __weak arch_irq_work_raise(void) * * Can be re-enqueued while the callback is still in progress. */ -bool irq_work_queue(struct irq_work *work) +static __always_inline bool +__irq_work_queue_on(struct irq_work *work, int cpu) { /* Only queue if not already pending */ if (!irq_work_claim(work)) @@ -78,16 +79,31 @@ bool irq_work_queue(struct irq_work *work) * for the next tick. */ if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) { - if (!this_cpu_cmpxchg(irq_work_raised, 0, 1)) - arch_irq_work_raise(); + if (cmpxchg(&__get_cpu_var(irq_work_raised, 0, 1) == 0)) { + if (cpu == smp_processor_id() || cpu == -1) + arch_irq_work_raise(); + else + arch_send_call_function_single_ipi(); + } } preempt_enable(); return true; } + +bool irq_work_queue(struct irq_work *work) +{ + return __irq_work_queue_on(work, -1); +} EXPORT_SYMBOL_GPL(irq_work_queue); +bool irq_work_queue_on(struct irq_work *work, int cpu) +{ + WARN_ON_ONCE(in_nmi()); + return __irq_work_queue_on(work, cpu); +} + bool irq_work_needs_cpu(void) { struct llist_head *this_list; diff --git a/kernel/smp.c b/kernel/smp.c index 06d574e42c72..0fd53963c4fb 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -198,6 +198,12 @@ void generic_smp_call_function_single_interrupt(void) csd->func(csd->info); csd_unlock(csd); } + + /* + * First run the synchronous callbacks, people are waiting on them; + * then run the async ones. + */ + irq_work_run(); } /*