linux-kernel - Re: [PATCH v4 1/3] powerpc: rewrite LOAD_REG

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Date:   Wed, 28 Aug 2019 14:24:49 +1000 (AEST)
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, segher@...nel.crashing.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] powerpc: rewrite LOAD_REG_IMMEDIATE() as an intelligent macro

On Tue, 2019-08-20 at 14:34:12 UTC, Christophe Leroy wrote:
> Today LOAD_REG_IMMEDIATE() is a basic #define which loads all
> parts on a value into a register, including the parts that are NUL.
> 
> This means always 2 instructions on PPC32 and always 5 instructions
> on PPC64. And those instructions cannot run in parallele as they are
> updating the same register.
> 
> Ex: LOAD_REG_IMMEDIATE(r1,THREAD_SIZE) in head_64.S results in:
> 
> 3c 20 00 00     lis     r1,0
> 60 21 00 00     ori     r1,r1,0
> 78 21 07 c6     rldicr  r1,r1,32,31
> 64 21 00 00     oris    r1,r1,0
> 60 21 40 00     ori     r1,r1,16384
> 
> Rewrite LOAD_REG_IMMEDIATE() with GAS macro in order to skip
> the parts that are NUL.
> 
> Rename existing LOAD_REG_IMMEDIATE() as LOAD_REG_IMMEDIATE_SYM()
> and use that one for loading value of symbols which are not known
> at compile time.
> 
> Now LOAD_REG_IMMEDIATE(r1,THREAD_SIZE) in head_64.S results in:
> 
> 38 20 40 00     li      r1,16384
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Series applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/c691b4b83b6a348f7b9d13c36916e73c2e1d85e4

cheers