linux-kernel - Re: [RFC 0/3] ARM: copy_{from,to}

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Message-ID: <nycvar.YSQ.7.77.849.2006121117250.3341460@knanqh.ubzr>
Date:   Fri, 12 Jun 2020 11:19:23 -0400 (EDT)
From:   Nicolas Pitre <nico@...xnic.net>
To:     afzal mohammed <afzal.mohd.ma@...il.com>
cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [RFC 0/3] ARM: copy_{from,to}_user() for vmsplit 4g/4g

On Fri, 12 Jun 2020, afzal mohammed wrote:

> Performance wise, results are not encouraging, 'dd' on tmpfs results,
> 
> ARM Cortex-A8, BeagleBone White (256MiB RAM):
> w/o series - ~29.5 MB/s
> w/ series - ~20.5 MB/s
> w/ series & highmem disabled - ~21.2 MB/s
> 
> On Cortex-A15(2GiB RAM) in QEMU:
> w/o series - ~4 MB/s
> w/ series - ~2.6 MB/s
> 
> Roughly a one-third drop in performance. Disabling highmem improves
> performance only slightly.

Could you compare with CONFIG_UACCESS_WITH_MEMCPY as well?


Nicolas