Date: Tue, 5 Jan 2010 16:34:45 -0600 (CST)
From: Christoph Lameter <cl@linux-foundation.org>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
cc: Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [RFC local_t removal V1 0/4] Remove local_t
In-Reply-To: <20100105222351.GA29675@Krystal>
Message-ID: <alpine.DEB.2.00.1001051629550.9108@router.home>
References: <20100105220417.400092933@quilx.com> <20100105222351.GA29675@Krystal>
User-Agent: Alpine 2.00 (DEB 1167 2008-08-23)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1832
Lines: 53

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.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/