[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20130829143053.3fc2caa8@gandalf.local.home>
Date: Thu, 29 Aug 2013 14:30:53 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Christoph Lameter <cl@...ux.com>
Cc: Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
Ingo Molnar <mingo@...hat.com>, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [gcv v3 06/35] scheduler: Replace __get_cpu_var uses
On Thu, 29 Aug 2013 18:15:43 +0000
Christoph Lameter <cl@...ux.com> wrote:
> On Thu, 29 Aug 2013, Steven Rostedt wrote:
>
> Its not really an atomic operation in the classic sense.
It doesn't need to be atomic, it could mean it is used within atomic
locations. Basically, "can't be interrupted here". I just said
"something like", it didn't even need to be that.
>
> this_cpu_no_preempt_check_read ?
I would make it much shorter. You could use "raw_this_cpu_read()",
which usually means "no checks here". Or, "this_cpu_read_nopreempt()".
>
> The problem that I have is also that a kernel with preemption is not
> something that see anywhere these days. Looks more like an academic
> exercise? Does this really matter? All the distro I see use
Um, my paycheck depends on PREEMPT_RT working. And there's a lot of
interest in real PREEMPT by audio folks. It's no more an
academic exercise than people wanting really low kernel latency.
> PREEMPT_VOLUNTARY. Performance degradation is significant if massive
> amounts of checks and preempt disable/enable points are added to the
> kernel.
They are usually disabled for production systems. But we run a bunch of
tests with the debug checks enabled, which catch bugs before we ship a
kernel for a production system.
>
> Do we agree that it is necessary and useful to add another variant of
> this_cpu ops for this? The concern of having too many variants is no
> longer there? Adding another variant is not that difficult just code
> intensive.
How many places use the this_cpu_*() without preemption disabled? I
wouldn't think there's many. I never complained about another variant,
so you need to ask those that have. The tough question for me is what
that variant name should be ;-)
-- Steve
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists