linux-kernel - Re: [PATCH v3 9/9] asm-generic: reverse GENERIC_{STRNCPY_FROM, STRNLEN}

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Date:   Thu, 22 Jul 2021 16:01:39 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     linux-arch <linux-arch@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Brian Cain <bcain@...eaurora.org>,
        Chris Zankel <chris@...kel.net>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Christoph Hellwig <hch@....de>, Guo Ren <guoren@...nel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Helge Deller <deller@....de>, Jeff Dike <jdike@...toit.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Max Filippov <jcmvbkbc@...il.com>,
        Michal Simek <monstr@...str.eu>,
        Richard Weinberger <richard@....at>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        linux-csky@...r.kernel.org,
        "open list:QUALCOMM HEXAGON..." <linux-hexagon@...r.kernel.org>,
        linux-ia64@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        "open list:SYNOPSYS ARC ARCHITECTURE" 
        <linux-snps-arc@...ts.infradead.org>,
        linux-um <linux-um@...ts.infradead.org>,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>,
        "moderated list:H8/300 ARCHITECTURE" 
        <uclinux-h8-devel@...ts.sourceforge.jp>
Subject: Re: [PATCH v3 9/9] asm-generic: reverse GENERIC_{STRNCPY_FROM,
 STRNLEN}_USER symbols

On Thu, Jul 22, 2021 at 3:57 PM Johannes Berg <johannes@...solutions.net> wrote:
>
> >
> > The remaining architectures at the moment are: ia64, mips, parisc,
> > s390, um and xtensa. We should probably convert these as well, but
>
> I'm not sure it makes sense to convert um, the implementation uses
> strncpy(), and that should use the libc implementation, which is tuned
> for the actual hardware that the binary is running on, so performance
> wise that might be better.
>
> OTOH, maybe this is all in the noise given the huge syscall overhead in
> um, so maybe unifying it would make more sense.

Right, makes sense. I suppose if we end up converting mips and s390,
we should just do arch/um and the others as well for consistency, even
if that adds some overhead.

      Arnd