From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Josh Triplett <josh@joshtriplett.org>,
Oleg Nesterov <oleg@redhat.com>,
linux-kernel@vger.kernel.org, mingo@kernel.org,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org,
dhowells@redhat.com, edumazet@google.com, darren@dvhart.com,
fweisbec@gmail.com, sbw@mit.edu
Subject: Re: [PATCH tip/core/timers 2/4] timers: Reduce __run_timers() latency for empty list
Date: Wed, 15 Jan 2014 18:22:51 -0800 [thread overview]
Message-ID: <20140116022251.GP10038@linux.vnet.ibm.com> (raw)
In-Reply-To: <20140115154710.4281c978@gandalf.local.home>
On Wed, Jan 15, 2014 at 03:47:10PM -0500, Steven Rostedt wrote:
> On Wed, 15 Jan 2014 12:32:45 -0800
> Josh Triplett <josh@joshtriplett.org> wrote:
>
> > On Wed, Jan 15, 2014 at 06:38:58PM +0100, Oleg Nesterov wrote:
> > > forgot to mention...
> > >
> > > On 01/14, Paul E. McKenney wrote:
> > > >
> > > > +static bool catchup_timer_jiffies(struct tvec_base *base)
> > > > +{
> > > > +#ifdef CONFIG_NO_HZ_FULL
> > > > + if (!base->all_timers) {
> > > > + base->timer_jiffies = jiffies;
> > > > + return 1;
> > > > + }
> > > > +#endif /* #ifdef CONFIG_NO_HZ_FULL */
> > > > + return 0;
> > > > +}
> > >
> > > Do we really want ifdef?
> > >
> > > This check is cheap, and !CONFIG_NO_HZ_FULL case looks a bit
> > > strange because we still update ->all_timers for no reason.
> >
> > There's an easy way to improve this: instead of using an ifdef, put
> > "IS_ENABLED(CONFIG_NO_HZ_FULL) && " in the if condition.
>
> Why even bother with that? What's wrong with doing this check all the
> time? Looks like it will save of the normal case too.
Sold! I removed the ifdef.
Thanx, Paul
next prev parent reply other threads:[~2014-01-16 2:23 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-15 5:19 [PATCH v2 tip/core/timers] Crude timer-wheel latency hacks Paul E. McKenney
2014-01-15 5:20 ` [PATCH tip/core/timers 1/4] timers: Track total number of timers in list Paul E. McKenney
2014-01-15 5:20 ` [PATCH tip/core/timers 2/4] timers: Reduce __run_timers() latency for empty list Paul E. McKenney
2014-01-15 17:03 ` Oleg Nesterov
2014-01-15 17:10 ` Peter Zijlstra
2014-01-16 2:14 ` Paul E. McKenney
2014-01-15 17:38 ` Oleg Nesterov
2014-01-15 20:32 ` Josh Triplett
2014-01-15 20:47 ` Steven Rostedt
2014-01-16 2:22 ` Paul E. McKenney [this message]
2014-01-15 20:33 ` Josh Triplett
2014-01-16 2:23 ` Paul E. McKenney
2014-01-15 5:20 ` [PATCH tip/core/timers 3/4] timers: Reduce future __run_timers() latency for newly emptied list Paul E. McKenney
2014-01-15 17:08 ` Oleg Nesterov
2014-01-16 2:23 ` Paul E. McKenney
2014-01-15 20:54 ` Steven Rostedt
2014-01-15 23:41 ` Paul E. McKenney
2014-01-15 5:20 ` [PATCH tip/core/timers 4/4] timers: Reduce future __run_timers() latency for first add to empty list Paul E. McKenney
2014-01-15 17:24 ` Oleg Nesterov
2014-01-15 17:31 ` [PATCH 0/1] timers: internal_add_timer() should update ->next_timer if ->active_timers == 0 Oleg Nesterov
2014-01-15 17:31 ` [PATCH 1/1] " Oleg Nesterov
2014-01-15 20:56 ` Steven Rostedt
2014-01-16 2:10 ` Paul E. McKenney
2014-01-16 2:33 ` [PATCH tip/core/timers 4/4] timers: Reduce future __run_timers() latency for first add to empty list Paul E. McKenney
2014-01-15 22:22 ` [PATCH v2 tip/core/timers] Crude timer-wheel latency hacks Thomas Gleixner
2014-01-16 2:36 ` Paul E. McKenney
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