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

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Message-Id: <20101029.133759.48489968.davem@davemloft.net>
Date:	Fri, 29 Oct 2010 13:37:59 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	rostedt@...dmis.org
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	akpm@...ux-foundation.org, fweisbec@...il.com, jbaron@...hat.com,
	ddaney@...iumnetworks.com
Subject: Re: [PATCH 4/8] jump label: Make arch_jump_label_text_poke_early()
 optional

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