linux-kernel - Re: [PATCH] jffs2: implement mount option to configure endianness

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Date:   Thu, 08 Nov 2018 19:47:08 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     "Nikunj Kela (nkela)" <nkela@...co.com>,
        Richard Weinberger <richard.weinberger@...il.com>
Cc:     "linux-mtd @ lists . infradead . org" <linux-mtd@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "xe-linux-external(mailer list)" <xe-linux-external@...co.com>
Subject: Re: [PATCH] jffs2: implement mount option to configure endianness

On Thu, 2018-11-08 at 18:01 +0000, Nikunj Kela (nkela) wrote:
>     But we can hypothesise and handwave about it until the cows come home;
>     I'd like to see a real test of whether it actually makes a difference
>     that we care about.
>     
>     If it does, one option might be to just build separate versions of
>     scan.c for each endianness, since that's the critical path we care
>     about.
> 
> I wonder if this feature is really that important that we need to duplicate the drivers.
> Also, it might take some time for me to find some device that I can run the tests with and without this patch.

Hm?

# modprobe mtdram size=16384
# mount -tjffs2 mtd0 /mnt
# cp -av .git /mnt # until it fills up
# umount /mnt
# perf record mount -tjffs2 mtd0 /mnt

On my desktop 'perf' only gets about 12 samples from that, so it's not
ideal. But you can make the mtdram device bigger, use something other
than my shiny new laptop, and use a higher sample frequency from 'perf'
and you should be able to get some vaguely meaningful results.


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