From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Dietmar Eggemann" <dietmar.eggemann@arm.com>,
"Michel Dänzer" <michel@daenzer.net>,
"Ingo Molnar" <mingo@redhat.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: Random panic in load_balance() with 3.16-rc
Date: Wed, 23 Jul 2014 20:25:18 +0200 [thread overview]
Message-ID: <20140723182518.GD3935@laptop> (raw)
In-Reply-To: <CA+55aFzDWritxv5RiqwcZ1qCKJQKK-Lw6StYFF7qx5YWgiCUTQ@mail.gmail.com>
On Wed, Jul 23, 2014 at 10:26:21AM -0700, Linus Torvalds wrote:
> On Wed, Jul 23, 2014 at 10:12 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > sched_init() definitely does _not_ allocate a cpumask_var.
>
> Side note: another good rule of thumb for per-cpu variables is:
>
> - if you use __get_cpu_var() without taking the address of it, you're
> doing something wrong and stupid.
>
> The whole - and really *only* - point of __get_cpu_var is to get the
> address of a a cpu variable. If you want to read the *value* of the
> variable, you should use "this_cpu_read()", which can use things like
> special instructions or segments to read the percpu area.
I think this code predates all the this_cpu* magic. But yes, agreed.
> I agree that the interface is not all that great, there's historical
> baggage there. We would have been better off with
> "__this_cpu_ptr(var)" instead of "&__get_cpu_var(var)". But that
> "__get_cpu_var()" is the old way of doing things (predating the new
> and better "this_cpu_read/write/ops()" stuff), which is why we have
> that odd interface with "&__get_cpu_var()".
I think there's a whole bunch of patches by Christoph Lameter, queued by
TJ that remove all __get_cpu_var usage and eventually the interface.
next prev parent reply other threads:[~2014-07-23 18:25 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <53C77BB8.6030804@daenzer.net>
2014-07-17 7:58 ` Random panic in load_balance() with 3.16-rc Peter Zijlstra
2014-07-18 9:29 ` Michel Dänzer
2014-07-22 6:13 ` Michel Dänzer
2014-07-23 3:53 ` Michel Dänzer
2014-07-23 4:21 ` Linus Torvalds
2014-07-23 6:49 ` Peter Zijlstra
2014-07-23 8:05 ` Michel Dänzer
2014-07-23 8:28 ` Peter Zijlstra
2014-07-23 9:25 ` Peter Zijlstra
2014-07-23 9:31 ` Michel Dänzer
2014-07-23 9:45 ` Dietmar Eggemann
2014-07-23 11:11 ` Peter Zijlstra
2014-07-23 11:30 ` Peter Zijlstra
2014-07-23 14:24 ` Peter Zijlstra
2014-07-23 14:38 ` Michel Dänzer
2014-07-23 15:51 ` Linus Torvalds
[not found] ` <20140723155526.GW3935@laptop>
2014-07-23 16:54 ` Linus Torvalds
2014-07-23 17:03 ` Peter Zijlstra
2014-07-23 17:12 ` Linus Torvalds
2014-07-23 17:26 ` Linus Torvalds
2014-07-23 18:25 ` Peter Zijlstra [this message]
2014-07-23 18:35 ` Linus Torvalds
2014-07-23 18:41 ` Peter Zijlstra
2014-07-23 18:55 ` Linus Torvalds
2014-07-23 19:02 ` Peter Zijlstra
2014-07-23 19:20 ` Linus Torvalds
2014-07-24 1:43 ` Michel Dänzer
2014-07-24 18:47 ` Linus Torvalds
2014-07-24 18:59 ` Peter Zijlstra
2014-07-25 1:25 ` Michel Dänzer
2014-07-25 2:33 ` Linus Torvalds
2014-07-25 2:50 ` Nick Krause
2014-07-25 2:36 ` Nick Krause
2014-07-25 3:55 ` Alexei Starovoitov
2014-07-25 4:00 ` Nick Krause
2014-07-25 14:02 ` Steven Rostedt
2014-07-25 18:29 ` Linus Torvalds
2014-07-25 19:10 ` Steven Rostedt
2014-07-25 20:01 ` Linus Torvalds
2014-07-25 20:13 ` Steven Rostedt
2014-07-25 21:25 ` Jakub Jelinek
2014-07-26 18:28 ` Linus Torvalds
2014-07-26 18:39 ` Linus Torvalds
2014-07-26 19:35 ` Markus Trippelsdorf
2014-07-26 19:55 ` Theodore Ts'o
2014-07-26 20:20 ` Markus Trippelsdorf
2014-07-26 22:08 ` Jakub Jelinek
2014-07-26 19:56 ` Linus Torvalds
2014-07-26 20:03 ` Linus Torvalds
2014-07-26 20:19 ` Markus Trippelsdorf
2014-07-26 20:39 ` Linus Torvalds
2014-07-28 12:26 ` Frank Ch. Eigler
2014-07-28 13:10 ` Theodore Ts'o
2014-07-28 14:11 ` Frank Ch. Eigler
2014-07-28 16:45 ` Linus Torvalds
2014-07-28 17:27 ` Alexei Starovoitov
2014-07-28 18:09 ` Markus Trippelsdorf
2014-07-28 18:28 ` Linus Torvalds
2014-07-28 18:41 ` Markus Trippelsdorf
2014-07-29 8:58 ` Jakub Jelinek
2014-07-28 19:50 ` Theodore Ts'o
2014-07-28 3:47 ` Michel Dänzer
2014-07-28 16:48 ` Linus Torvalds
2014-07-29 2:29 ` Michel Dänzer
2014-08-05 3:19 ` Steven Rostedt
2014-07-26 18:02 ` Steven Chamberlain
2014-07-29 9:20 ` Michel Dänzer
2014-07-25 6:48 ` Jakub Jelinek
2014-07-25 8:15 ` Linus Torvalds
2014-07-25 9:03 ` Michel Dänzer
2014-07-25 9:21 ` Markus Trippelsdorf
2014-07-25 9:42 ` Markus Trippelsdorf
2014-07-23 18:07 ` Linus Torvalds
2014-07-23 18:31 ` Peter Zijlstra
2014-07-23 18:24 ` Peter Zijlstra
2014-07-23 17:04 ` Peter Zijlstra
2014-07-23 17:15 ` Linus Torvalds
2014-07-23 18:25 ` Peter Zijlstra
2014-07-23 18:23 ` Peter Zijlstra
2014-07-23 10:52 ` Peter Zijlstra
2014-07-24 7:18 ` Michel Dänzer
2014-07-24 7:51 ` Peter Zijlstra
2014-07-24 9:55 ` Peter Zijlstra
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