linux-kernel - Re: [PATCH 05/11] powerpc/8xx: Optimise access to swapper_pg

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Date:	Tue, 06 Jan 2015 14:27:38 +0100
From:	leroy christophe <christophe.leroy@....fr>
To:	David Laight <David.Laight@...LAB.COM>,
	'Joakim Tjernlund' <Joakim.Tjernlund@...nsmode.se>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"scottwood@...escale.com" <scottwood@...escale.com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 05/11] powerpc/8xx: Optimise access to swapper_pg_dir


Le 06/01/2015 13:08, David Laight a écrit :
>> On Tue, 2014-12-16 at 16:03 +0100, Christophe Leroy wrote:
>>> All accessed to PGD entries are done via 0(r11).
>>> By using lower part of swapper_pg_dir as load index to r11, we can remove the
>>> ori instruction.
>>>
>>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> Nice :)
>> Acked-by: Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
>>
>>> ---
>>>   arch/powerpc/kernel/head_8xx.S | 22 ++++++++++------------
>>>   1 file changed, 10 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
>>> index ae05f28..aa45225 100644
>>> --- a/arch/powerpc/kernel/head_8xx.S
>>> +++ b/arch/powerpc/kernel/head_8xx.S
>>> @@ -322,13 +322,12 @@ InstructionTLBMiss:
>>>          mfspr   r11, SPRN_M_TW/* Get level 1 table base address */
>>>   #ifdef CONFIG_MODULES
>>>          beq     3f
>>> -       lis     r11, (swapper_pg_dir-PAGE_OFFSET)@h
>>> -       ori     r11, r11, (swapper_pg_dir-PAGE_OFFSET)@l
>>> +       lis     r11, (swapper_pg_dir-PAGE_OFFSET)@ha
>>>   3:
>>>   #endif
>>>          /* Insert level 1 index */
>>>          rlwimi  r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
>>> -       lwz     r11, 0(r11)/* Get the level 1 entry */
>>> +       lwz     r11, (swapper_pg_dir-PAGE_OFFSET)@l(r11)/* Get the level 1 entry */
>>>
> On the face of it that fragment doesn't look right when CONFIG_MODULES is undefined.
>
> 	David
>
I'm not sure I understand what you mean.

The other part of the patch adds the following:
+    li    r5, (swapper_pg_dir-PAGE_OFFSET)@l
+    sub    r4, r4, r5

r4 is the value put into SPRN_M_TW, so I don't see what may be wrong.

Christophe
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