linux-kernel - Re: [RFC] arm64:change jump_label to use branch instruction, not use NOP instr

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Date:	Fri, 31 Jul 2015 11:33:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	yalin wang <yalin.wang2010@...il.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ingo Molnar <mingo@...nel.org>, anton@...ba.org,
	mark.rutland@....com, linux-arm-kernel@...ts.infradead.org,
	open list <linux-kernel@...r.kernel.org>, jbaron@...mai.com
Subject: Re: [RFC] arm64:change jump_label to use branch instruction, not use
 NOP instr

On Fri, Jul 31, 2015 at 05:25:02PM +0800, yalin wang wrote:
> 
> > On Jul 31, 2015, at 15:52, Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > On Fri, Jul 31, 2015 at 03:41:37PM +0800, yalin wang wrote:
> >> This change a little arch_static_branch(), use b . + 4 for false
> >> return, why? According to aarch64 TRM, if both source and dest
> >> instr are branch instr, can patch the instr directly, don't need
> >> all cpu to do ISB for sync, this means we can call
> >> aarch64_insn_patch_text_nosync() during patch_text(),
> >> will improve the performance when change a static_key.
> > 
> > This doesn't parse.. What?
> > 
> > Also, this conflicts with the jump label patches I've got.
> 
> this is arch depend , you can see aarch64_insn_patch_text( ) for more info,
> if aarch64_insn_hotpatch_safe() is true, will patch the text directly.

So I patched all arches, including aargh64.

> what is your git branch base? i make the patch based on linux-next branch,
> maybe a little delay than yours , could you share your branch git address?
> i can make a new based on yours .

https://git.kernel.org/cgit/linux/kernel/git/peterz/queue.git/log/?h=locking/jump_label

Don't actually use that branch for anything permanent, this is throw-away
git stuff.

But you're replacing a NOP with an unconditional branch to the next
instruction? I suppose I'll leave that to Will and co.. I just had
trouble understanding your Changelog -- also I was very much not awake
yet.


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