netdev - Re: [PATCH] percpu: add optimized generic percpu accessors

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Date:	Thu, 29 Jan 2009 13:33:13 -0500 (EST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Rusty Russell <rusty@...tcorp.com.au>, Tejun Heo <tj@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	akpm@...ux-foundation.org, hpa@...or.com, brgerst@...il.com,
	ebiederm@...ssion.com, travis@....com,
	linux-kernel@...r.kernel.org, steiner@....com, hugh@...itas.com,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] percpu: add optimized generic percpu accessors

On Wed, 28 Jan 2009, Mathieu Desnoyers wrote:

> > The term cpu is meaning multiple things at this point. So yes it may be
> > better to go with glibc naming of thread local space.
> >
>
> However using "local" for "per-cpu" could be confusing with the glibc
> naming of thread local space, because "per-thread" and "per-cpu"
> variables are different from a synchronization POV and we can end up
> needing both (e.g. a thread local variable can never be accessed by
> another thread, but a cpu local variable could be accessed by a
> different CPU due to scheduling).

gcc/glibc support a __thread attribute to variables. As far as I can tell
this automatically makes gcc perform the relocation to the current
context using a segment register.

But its a weird ABI http://people.redhat.com/drepper/tls.pdf. After
reading that I agree that we should stay with the cpu ops and forget about
the local and thread stuff in gcc/glibc.

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