linux-kernel - Re: x86: use this_cpu for debug_stack

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Message-ID: <0000014054f7bbe5-97cac4df-1811-4f3f-8bfe-8f754774e006-000000@email.amazonses.com>
Date:	Tue, 6 Aug 2013 18:50:56 +0000
From:	Christoph Lameter <cl@...two.org>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	linux-kernel@...r.kernel.org
Subject: Re: x86: use this_cpu for debug_stack_usage

On Tue, 6 Aug 2013, Steven Rostedt wrote:

> I don't remember why I didn't use this in the first place. Perhaps I was
> still in the "get_cpu" mind set.
>
> Also, what's the difference between "__this_cpu_inc()" and
> "this_cpu_inc()"?

The fallback logic for arches not supporting segment prefixes is differnt.
this_cpu_inc() disables interrupts.

__this_cpu_inc() is used when you know that the scheduler cannot move the
process.

The code generated by both is the same on x86.

> >  int is_debug_stack(unsigned long addr);
> >  void debug_stack_set_zero(void);
>
> Might as well change is_debug_stack() to use __this_cpu_read() instead
> of __get_cpu_var().

True and that will also shave off some instructions.

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