Re: [PATCH] RFC x86_64 more accurate KSTK_ESP implementation

From: Andi Kleen <andi@firstfloor.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Stefani Seibold <stefani@seibold.net>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Americo Wang <xiyou.wangcong@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] RFC x86_64 more accurate KSTK_ESP implementation
Date: Sun, 08 Nov 2009 20:37:50 +0100	[thread overview]
Message-ID: <87639k7qpd.fsf@basil.nowhere.org> (raw)
In-Reply-To: <20091108113546.GN11372@elte.hu> (Ingo Molnar's message of "Sun, 8 Nov 2009 12:35:46 +0100")

Ingo Molnar <mingo@elte.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@linux.intel.com -- Speaking for myself only.