Message-ID: <1430331905.8722.16.camel@j-VirtualBox>
Subject: Re: [PATCH v2 1/5] sched, timer: Remove usages of ACCESS_ONCE in
 the scheduler
From: Jason Low <jason.low2@hp.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Waiman Long <waiman.long@hp.com>, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        Scott J Norton <scott.norton@hp.com>, jason.low2@hp.com
Date: Wed, 29 Apr 2015 11:25:05 -0700
In-Reply-To: <20150429131532.15443d08@gandalf.local.home>
References: <1430251224-5764-1-git-send-email-jason.low2@hp.com>
	 <1430251224-5764-2-git-send-email-jason.low2@hp.com>
	 <55410F73.5000807@hp.com> <20150429131532.15443d08@gandalf.local.home>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1414
Lines: 41

On Wed, 2015-04-29 at 13:15 -0400, Steven Rostedt wrote:
> On Wed, 29 Apr 2015 13:05:55 -0400
> Waiman Long <waiman.long@hp.com> wrote:
> 
> > >   		goto no_join;
> > > @@ -2107,7 +2107,7 @@ void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
> > >
> > >   static void reset_ptenuma_scan(struct task_struct *p)
> > >   {
> > > -	ACCESS_ONCE(p->mm->numa_scan_seq)++;
> > > +	WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
> > >   	p->mm->numa_scan_offset = 0;
> > >   }
> > >
> > >
> > 
> > Generally, I am for replacing ACCESS_ONCE() with the more descriptive 
> > READ_ONCE() and WRITE_ONCE() except the above case where it makes the 
> > code harder to read without any real advantage.
> > 
> > Other than that,
> > 
> > Acked-by: Waiman Long <Waiman.Long@hp.com>
> > 
> 
> I agree, but I believe this code needs to be updated anyway. Making it
> uglier may encourage that to happen.

Yep, in this case, the ACCESS_ONCE conversion on numa_scan_seq
technically isn't necessary, but I think the best option is to
consistently update all of them, which makes things clearer than using
multiple sets of APIs.

Thanks,
Jason

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/