linux-kernel - Re: [RFC local_t removal V1 0/4] Remove local

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Date:	Tue, 5 Jan 2010 16:34:45 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC local_t removal V1 0/4] Remove local_t

On Tue, 5 Jan 2010, Mathieu Desnoyers wrote:

> Yes, removing the local_t type could make sense. However, local_t maps
> to a volatile long, not just "long". Secondly, I am concerned about the
> fact that the patch you propose:

Volatile is discouraged as far as I can tell.

> - does not create the primitives I use in lttng
> - only deals with x8

As I said its an RFC. This provides all the functionality you need
through. The rest is sugar coating.

> In lttng (which is out of tree, but widely used), I need the equivalent
> of:
>
> local_read
> local_set
> local_add
> local_cmpxchg
> local_add_return
> local_inc

Please read the patch! This is all provided. add_local_return in the RFC
provides what is needed to replace local_add, local_inc. We can add these
explicitly.

local_cmpxchg replacement is already in there in the form of
cmpxchg_local().

> The approach of just doing the x86 implementation and leaving all the
> other architectures "for later" with a slow/non atomic generic fallback
> is, imho, a no-go, given that some people (myself, actually) already
> took the time to go through all the kernel architectures to create the
> optimized local.h headers. Basically, you are destroying all that work,
> asking for it to be done all over again.

AS I said this is an RFC. I can easily generate all these things from the
existing local.hs for the architectures.

> I therefore argue that we should keep local.h as-is as long as the
> replacement lacks the wide architecture support and primitive variety
> found in local.h.

Cool down and please review the patch.


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