linux-kernel - Re: [guv v2 04/31] net: Replace __get_cpu

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Message-Id: <20130902.203355.117341085023152754.davem@davemloft.net>
Date:	Mon, 02 Sep 2013 20:33:55 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dhowells@...hat.com
Cc:	cl@...ux.com, tj@...nel.org, akpm@...uxfoundation.org,
	netdev@...r.kernel.org, linux-arch@...r.kernel.org,
	srostedt@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [guv v2 04/31] net: Replace __get_cpu_var uses

From: David Howells <dhowells@...hat.com>
Date: Mon, 02 Sep 2013 22:35:06 +0100

> Would it be possible to use __thread annotations for per-CPU
> variables, I wonder?

Paul Mackerras tried it on powerpc and you can't do it.

The problem is that there is no way to tell the compiler that sched()
and similar (potentially) change the thread pointer base.

It really will cache pre-computed __thread pointer calculations across
sched().
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