Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH 4/4] powerpc/32: remove a NOP from memset() | Date | Fri, 25 Aug 2017 10:15:08 +1000 |
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Christophe LEROY <christophe.leroy@c-s.fr> writes:
> Le 24/08/2017 à 12:51, Michael Ellerman a écrit : >> 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. > > Unfortunately, as we discussed in 2015 > (https://lkml.org/lkml/2015/9/10/608),
Haha, you expect me to remember things I said then! ;)
> the ALT_FTR does things too early, while the cache is not enabled yet.
OK. Ben did do some reworks to the early init since then, but I don't think he changed that.
I notice we do setup_feature_keys() in machine_init(), which is the jump label equivalent of apply_feature_fixups(). So I wonder if we could actually move apply_feature_fixups() to there. But it would need some serious review.
cheers
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