linux-kernel - Re: [PATCH v2] powerpc/uaccess: Use flexible addressing with __put_user()/__get

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Message-ID: <20200812193032.GU6753@gate.crashing.org>
Date:   Wed, 12 Aug 2020 14:30:32 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, npiggin@...il.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()

On Wed, Aug 12, 2020 at 02:32:51PM +0200, Christophe Leroy wrote:
> Anyway, it seems that GCC doesn't make much use of the "m<>" and the 
> pre-update form.

GCC does not use update form outside of inner loops much.  Did you
expect anything else?

> Most of the benefit of flexible addressing seems to be 
> achieved with patch 1 ie without the "m<>" constraint and update form.

Yes.


Segher