linux-kernel - Re: [PATCH 05/10] smp: Fast path check on IPI list

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140729215536.GC14520@localhost.localdomain>
Date:	Tue, 29 Jul 2014 23:55:37 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH 05/10] smp: Fast path check on IPI list

On Tue, Jul 29, 2014 at 02:07:39PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 28, 2014 at 07:37:31PM +0200, Frederic Weisbecker wrote:
> > When we enqueue a remote irq work, we trigger the same IPI as those
> > raised by smp_call_function_*() family.
> > 
> > So when we receive such IPI, we check both irq_work and smp_call_function
> > queues. Thus if we trigger a remote irq work, we'll likely find the
> > smp_call_function queue empty unless we collide with concurrent enqueuers
> > but the probability is low.
> > 
> > Meanwhile, checking the smp_call_function queue can be costly because
> > we use llist_del_all() which relies on cmpxchg().
> 
> xchg()

It's still costly though as it's an atomic read/write with full barrier. I'll
update the comment meanwhile.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/