Date: Thu, 27 Aug 2015 23:12:21 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Jason Low <jason.low2@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Oleg Nesterov <oleg@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Terry Rudd <terry.rudd@hp.com>, Rik van Riel <riel@redhat.com>,
        Scott J Norton <scott.norton@hp.com>
Subject: Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention
Message-ID: <20150827211219.GA25501@lerouge>
References: <1440559068-29680-1-git-send-email-jason.low2@hp.com>
 <1440559068-29680-4-git-send-email-jason.low2@hp.com>
 <20150826225628.GD11992@lerouge>
 <1440631954.32300.26.camel@j-VirtualBox>
 <20150827125300.GA21105@lerouge>
 <1440707390.32300.100.camel@j-VirtualBox>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1440707390.32300.100.camel@j-VirtualBox>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1321
Lines: 42

On Thu, Aug 27, 2015 at 01:29:50PM -0700, Jason Low wrote:
> On Thu, 2015-08-27 at 14:53 +0200, Frederic Weisbecker wrote:
> > Sure, like:
> > 
> > #define CPUTIMER_RUNNING 0x1
> > #define CPUTIMER_CHECKING 0x2
> > 
> > struct thread_group_cputimer {
> >     struct task_cputime_atomic cputime_atomic;
> >     int status;
> > }
> > 
> > So from cputimer_running() you just need to check:
> > 
> >      if (cputimer->status & CPUTIMER_RUNNING)
> > 
> > And from run_posix_cpu_timer() fast-path:
> > 
> >      if (cputimer->status == CPUTIMER_RUNNING)
> > 
> > so that ignores CPUTIMER_CHECKING case.
> 
> Right, having just 1 "status" field can simply things a bit. The
> (cputimer->status == CPUTIMER_RUNNING) check does appear misleading
> though, since we're technically not only checking for if the "cputimer
> is running".
> 
> Maybe something like:
> 
> int status = cputimer->status;
> if ((status & CPUTIMER_RUNNING) && !(status & CPUTIMER_CHECKING))
> 
> makes it more obvious what's going on here.

The result is the same but it may clarify the code indeed.

Thanks.
--
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/