linux-kernel - Re: [PATCH] RFC x86_64 more accurate KSTK

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Date:	Sun, 08 Nov 2009 20:37:50 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Stefani Seibold <stefani@...bold.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Americo Wang <xiyou.wangcong@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] RFC x86_64 more accurate KSTK_ESP implementation

Ingo Molnar <mingo@...e.hu> writes:
>
> I'd suggest a competely different method: why dont you use an IPI to 
> sample the SP whenever someone wants to read it from /proc and we see 
> that the task is running on a CPU right now?

Most of /proc tends to turn into a fast path when you run the right
monitoring tools unfortunately, which poll /proc at sometimes
quite high frequencies.

I suspect you'll slow something down significantly with this approach.

The only good way to avoid that would be to use a separate file, but again
if someone really wants it they can as well just use a ptrace()
based program from user space.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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