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Date:   Fri, 12 Jun 2020 11:19:23 -0400 (EDT)
From:   Nicolas Pitre <nico@fluxnic.net>
To:     afzal mohammed <afzal.mohd.ma@gmail.com>
cc:     Russell King - ARM Linux admin <linux@armlinux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [RFC 0/3] ARM: copy_{from,to}_user() for vmsplit 4g/4g
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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