linux-kernel - Re: [RFC PATCH v1] power: don't manage floating point regs when no FPU

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Message-ID: <9edf75a2-103d-ea01-2f53-dbb467047d13@csgroup.eu>
Date:   Tue, 11 Aug 2020 15:48:07 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v1] power: don't manage floating point regs when no
 FPU



Le 11/08/2020 à 14:07, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>> There is no point in copying floating point regs when there
>> is no FPU and MATH_EMULATION is not selected.
> 
> Yeah I guess you're right. I've never touched a system with neither, but
> if such a thing exists then it does seem silly to copy regs around that
> can't be used.

Yes that exists, because glibc implements floating point emulation and 
it is definitely more efficient to rely of glibc emulation than kernel one.

>>   10 files changed, 44 insertions(+), 1 deletion(-)
> 
> In general this looks fine.
> 
> It's a bit #ifdef heavy. Maybe some of those can be cleaned up a bit
> with some wrapper inlines?
> 

Yes I'll try and respin, as part of a series I'm preparing to switch the 
32 bits signal code to using user_access_begin() logic and 
unsafe_put_user() and friends to reduce KUAP unlock/lock.

Christophe