From: Andrew Morton <akpm@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
Alessio Igor Bogani <abogani@kernel.org>,
Chris Metcalf <cmetcalf@tilera.com>,
Christoph Lameter <cl@linux.com>,
Geoff Levand <geoff@infradead.org>,
Gilad Ben Yossef <gilad@benyossef.com>,
Hakan Akkan <hakanakkan@gmail.com>,
Ingo Molnar <mingo@kernel.org>,
Li Zhong <zhong@linux.vnet.ibm.com>,
Namhyung Kim <namhyung.kim@lge.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v4] context_tracking: Add comments on interface and internals
Date: Wed, 16 Jan 2013 14:06:48 -0800 [thread overview]
Message-ID: <20130116140648.e5e93ac7.akpm@linux-foundation.org> (raw)
In-Reply-To: <1358372961.23211.8.camel@gandalf.local.home>
On Wed, 16 Jan 2013 16:49:21 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Wed, 2013-01-16 at 13:18 -0800, Andrew Morton wrote:
> > On Wed, 16 Jan 2013 17:16:37 +0100
>
> > I still don't understand NOHZ's role in this whole thing :(
>
> It's not for idle NOHZ, but "process" NOHZ.
>
> That is if we have only one task running on a CPU, we don't want a tick
> interrupt to bother it. This is because there's lots of users out there
> that want an uninterrupted task. A task that doesn't ever get bothered
> by the kernel. If it's in userspace, it stays in userspace (no
> interrupts), until it calls into the kernel itself (syscall). Even when
> its in the kernel, we still don't need the tick interrupt if its the
> only task.
oh, is that what TIF_NOHZ does ;)
> But the scheduler isn't the only thing that uses this tick. To remove
> the tick, we need to satisfy all the other users (printk, delayed work,
> u/s-times).
>
> To still keep up the stats of user and kernel times for the task, we
> need to record when the task switches from user to kernel and back
> again. Hence the context tracking code.
>
> Makes more sense?
yup thanks.
prev parent reply other threads:[~2013-01-16 22:06 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-16 12:32 [PATCH] context_tracking: Add comments on interface and internals Frederic Weisbecker
2013-01-16 13:04 ` Namhyung Kim
2013-01-16 14:58 ` Frederic Weisbecker
2013-01-16 16:16 ` [PATCH v4] " Frederic Weisbecker
2013-01-16 21:18 ` Andrew Morton
2013-01-16 21:49 ` Steven Rostedt
2013-01-16 22:06 ` Andrew Morton [this message]
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