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From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@c-s.fr>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>, Scott Wood <oss@buserror.net>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 4/4] powerpc/32: remove a NOP from memset()
Date: Thu, 24 Aug 2017 20:51:03 +1000	[thread overview]
Message-ID: <871so1w86g.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <ae2205dedfe437e4df2dd0cc7605d62189833221.1503277387.git.christophe.leroy@c-s.fr>

Christophe Leroy <christophe.leroy@c-s.fr> writes:

> memset() is patched after initialisation to activate the
> optimised part which uses cache instructions.
>
> Today we have a 'b 2f' to skip the optimised patch, which then gets
> replaced by a NOP, implying a useless cycle consumption.
> As we have a 'bne 2f' just before, we could use that instruction
> for the live patching, hence removing the need to have a
> dedicated 'b 2f' to be replaced by a NOP.
>
> This patch changes the 'bne 2f' by a 'b 2f'. During init, that
> 'b 2f' is then replaced by 'bne 2f'

I'm not sure what the sequence is during boot for the 32-bit code, but
can you use an ALT_FTR section for this? Possibly that doesn't get done
at the right time though.

cheers

  reply	other threads:[~2017-08-24 10:51 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-23 14:54 [PATCH 0/4] powerpc/32: memset() optimisations Christophe Leroy
2017-08-23 14:54 ` [PATCH 2/4] powerpc: fix location of two EXPORT_SYMBOL Christophe Leroy
2017-08-23 14:54 ` [PATCH 3/4] powerpc/32: optimise memset() Christophe Leroy
2017-08-23 14:54 ` [PATCH 4/4] powerpc/32: remove a NOP from memset() Christophe Leroy
2017-08-24 10:51   ` Michael Ellerman [this message]
2017-08-24 13:58     ` Christophe LEROY
2017-08-25  0:15       ` Michael Ellerman

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