From: Oleg Nesterov <oleg@redhat.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com,
edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com,
sbw@mit.edu
Subject: Re: [PATCH tip/core/timers 1/3] timers: Reduce __run_timers() latency for empty list
Date: Wed, 15 Jan 2014 17:25:31 +0100 [thread overview]
Message-ID: <20140115162531.GA11499@redhat.com> (raw)
In-Reply-To: <20140114235015.GZ10038@linux.vnet.ibm.com>
On 01/14, Paul E. McKenney wrote:
>
> On Tue, Jan 14, 2014 at 07:48:28PM +0100, Oleg Nesterov wrote:
> > > __internal_add_timer(struct tvec_base *base, struct timer_list *timer)
> > > {
> > > @@ -1146,6 +1157,10 @@ static inline void __run_timers(struct tvec_base *base)
> > > struct timer_list *timer;
> > >
> > > spin_lock_irq(&base->lock);
> >
> > Do we really need to take base->lock before catchup_timer_jiffies() ?
> > ->timer_jiffies can only be changed by us, and it seems that we do
> > not care if we race with base->active_timers++.
>
> Given that this lock should be almost always acquired by the current
> CPU, the penalty for acquiring it should be low. After all, we were
> acquiring it prior to this patch as many times as we are after this patch,
> right?
Yes. But
if (catchup_timer_jiffies())
return;
looks a bit simpler and can save a couple of insn. I won't argue of course,
this is minor. And you already sent v2, I'll try add some comments...
Oleg.
prev parent reply other threads:[~2014-01-15 16:26 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-14 4:14 [PATCH tip/core/rcu 0/3] Crude timer-wheel latency hacks Paul E. McKenney
2014-01-14 4:15 ` [PATCH tip/core/timers 1/3] timers: Reduce __run_timers() latency for empty list Paul E. McKenney
2014-01-14 4:15 ` [PATCH tip/core/timers 2/3] timers: Reduce future __run_timers() latency for newly emptied list Paul E. McKenney
2014-01-14 4:15 ` [PATCH tip/core/timers 3/3] timers: Reduce future __run_timers() latency for first add to empty list Paul E. McKenney
2014-01-14 18:48 ` [PATCH tip/core/timers 1/3] timers: Reduce __run_timers() latency for " Oleg Nesterov
2014-01-14 23:50 ` Paul E. McKenney
2014-01-15 16:25 ` Oleg Nesterov [this message]
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