Le 12/09/2022 à 17:22, Christophe Leroy a écrit :
Le 12/09/2022 à 15:46, Lukas Bulwahn a écrit :
Hi Joe, hi Ben,
While reviewing some kernel config, I came across
CONFIG_DCACHE_WORD_ACCESS and tried to understand its purpose.
Then, I discovered this RFC patch from 2014 that seems never to have
been integrated:
https://lore.kernel.org/all/1393964591.20435.58.camel@joe-AO722/
[RFC] Remove CONFIG_DCACHE_WORD_ACCESS
The discussion seemed to just not continue and the patch was just not
integrated by anyone.
In the meantime, the use of CONFIG_DCACHE_WORD_ACCESS has spread into
a few more files, but replacing it with
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS still seems feasible.
Are you aware of reasons that this patch from 2014 should not be
integrated?
I would spend some time to move the integration of this patch further
if you consider that the patch is not completely wrong.
As far as I can see, for the time being this is not equivalent on powerpc:
select HAVE_EFFICIENT_UNALIGNED_ACCESS if !(CPU_LITTLE_ENDIAN &&
POWER7_CPU)
select DCACHE_WORD_ACCESS if PPC64 && CPU_LITTLE_ENDIAN
This will need to be investigated I guess.
In the meantime I'll try to see if it makes any difference for ppc32.
Selecting DCACHE_WORD_ACCESS on powerpc32 provides an improvement of
approx 9% on a powerpc 8xx and about 2% on a powerpc 832x, using the
benchmark test in commit a75c380c7129 ("powerpc: Enable
DCACHE_WORD_ACCESS on ppc64le")
Christophe
