linux-kernel - Re: [PATCH 4/8] jump label: Make arch_jump_label_text_poke

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Date:	Fri, 29 Oct 2010 13:48:31 -0700
From:	David Daney <ddaney@...iumnetworks.com>
To:	David Miller <davem@...emloft.net>
CC:	rostedt@...dmis.org, linux-kernel@...r.kernel.org, mingo@...e.hu,
	akpm@...ux-foundation.org, fweisbec@...il.com, jbaron@...hat.com
Subject: Re: [PATCH 4/8] jump label: Make arch_jump_label_text_poke_early()
 optional

On 10/29/2010 01:37 PM, David Miller wrote:
> From: Steven Rostedt<rostedt@...dmis.org>
> Date: Thu, 28 Oct 2010 09:55:52 -0400
>
>> From: David Daney<ddaney@...iumnetworks.com>
>>
>> For the forthcoming MIPS jump label support,
>> arch_jump_label_text_poke_early() is unneeded as the MIPS NOP
>> instruction is already optimal.
>>
>> Supply a default implementation that does nothing.  Flag x86 and SPARC
>> as having arch_jump_label_text_poke_early().
>>
>> Cc: Jason Baron<jbaron@...hat.com>
>> Cc: David Miller<davem@...emloft.net>
>> Signed-off-by: David Daney<ddaney@...iumnetworks.com>
>> LKML-Reference:<1286218615-24011-2-git-send-email-ddaney@...iumnetworks.com>
>> Signed-off-by: Steven Rostedt<rostedt@...dmis.org>
>
> On the SPARC side, it's not that the nop isn't optimal, on sparc it's
> always 0x01000000.

That's what I thought.  You could remove your
arch_jump_label_text_poke_early() function to no determent.

> The issue is that when written an I-cache flush is
> necessary using a 'flushi' instruction.
>
> Does MIPS not need a flush when poking instructions?

Yes, it does.

> I find this hard to believe, although it's been some time since I
> last touched that architecture :-)

I just looked at my patch again.  I am indeed flushing the I cache
after patching the code, so I don't really know what you are talking
about.

David Daney
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