linux-kernel - Re: [PATCH 08/12] powerpc/ftrace: Rework ftrace

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Message-ID: <20160225142554.GI21932@lst.de>
Date:	Thu, 25 Feb 2016 15:25:54 +0100
From:	Torsten Duwe <duwe@....de>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	linuxppc-dev@...abs.org, bsingharora@...il.com,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	kamalesh@...ux.vnet.ibm.com, pmladek@...e.com, jeyu@...hat.com,
	jkosina@...e.cz, live-patching@...r.kernel.org, mbenes@...e.cz
Subject: Re: [PATCH 08/12] powerpc/ftrace: Rework ftrace_caller()

On Thu, Feb 25, 2016 at 01:28:31AM +1100, Michael Ellerman wrote:
> The main change is to just use paca->kernel_toc, rather than a branch to
> +4 and mflr etc. That makes the code simpler and should also perform
> better.

Indeed.

> There was also a sequence after ftrace_call() where we load from
> pt_regs->nip, move to LR, then a few instructions later load from LRSAVE
> and move to LR. Instead I think we want to put pt_regs->nip into CTR and
> branch to it later.

Yes, I did some of this cleanup in the livepatch implementation.

> We also rework some of the SPR loads to hopefully speed them up a bit.
> Also comment the asm much more, to hopefully make it clearer.
> 
> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>

Reviewed-by: Torsten Duwe <duwe@...e.de>

	Torsten