linux-kernel - Re: [PATCH] lib: memmove: Use optimised memcpy if possible

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Date:   Sun, 26 Nov 2017 18:21:36 +0530
From:   PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     open list <linux-kernel@...r.kernel.org>, mchehab@...nel.org,
        Paul Burton <paul.burton@...tec.com>
Subject: Re: [PATCH] lib: memmove: Use optimised memcpy if possible

Hi Dan,

On 26 November 2017 at 02:10, Dan Carpenter <dan.carpenter@...cle.com> wrote:
> Paul's original patch should have been separated into two patches to
> begin with.  The patch does two different things and one part goes
> through the MIPS tree and one part goes through Andrew, probably.

Okay. I will split his patch into two and send with my modifications.

> On Sat, Nov 25, 2017 at 10:52:04PM +0530, PrasannaKumar Muralidharan wrote:
>> Hi,
>>
>> On 4 October 2017 at 22:26, PrasannaKumar Muralidharan
>> <prasannatsmkumar@...il.com> wrote:
>> > When there is no overlap between src and dst use optimised memcpy if it
>> > is available.
>> >
>> > Signed-off-by: Paul Burton <paul.burton@...tec.com>
>> > Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
>> > ---
>> > This change is a small part of a patch [1] from Paul Burton. I have
>> > added his Signed-off by. I do not know whether it is correct. Please let
>> > me know if it has to be changed, I will send a v2.
>
>
> Sign-off is like signing a legal document.  Read
> Documentation/process/submitting-patches.rst the section about
> "11) Sign your work - the Developer's Certificate of Origin" for an
> explanation.
>
> So, yeah, Paul provided his s-o-b and it needs to be here as well.  But
> also he maybe should get authorship credit.  Just put the first line in
> the email as:
>
> From: Paul Burton <paul.burton@...tec.com>
>
> But that's sort of a trickier thing, so maybe put some explanation that
> you chopped out a bit from Pauls patch in the changelog:
>
>         This is part of a patch that Paul Burton wrote
>         https://patchwork.linux-mips.org/patch/14517/
>
> I know you put that here, but since it's under the --- cut off it won't
> be saved in the final git log.

Sure. Will do.

>> >
>> > This patch is boot tested with qemu for MIPS architecture by removing
>> > mips's memmove routine. This patch does not contain MIPS changes. I
>> > will try to find out why [1] was not taken already and figure out what
>> > to do.
>> >
>
> Instead of boot testing, it would be better if we had a benchmark to
> show it helped speed things up.

I will try to come up with some reasonable benchmark and post its results.

>> > 1. https://patchwork.linux-mips.org/patch/14517/
>> >
>> >  lib/string.c | 11 +++++++++++
>> >  1 file changed, 11 insertions(+)
>> >
>> > diff --git a/lib/string.c b/lib/string.c
>> > index 9921dc2..462ab7b 100644
>> > --- a/lib/string.c
>> > +++ b/lib/string.c
>> > @@ -825,6 +825,17 @@ void *memmove(void *dest, const void *src, size_t count)
>> >         char *tmp;
>> >         const char *s;
>> >
>> > +#ifdef __HAVE_ARCH_MEMCPY
>> > +       /* Use optimised memcpy when there is no overlap */
>> > +       const char *s_end = src + count;
>> > +       const char *d = dest;
>> > +       char *d_end = dest + count;
>> > +
>> > +       s = src;
>> > +       if ((d_end <= s) || (s_end <= d))
>> > +               return memcpy(dest, src, count);
>> > +#endif /* __HAVE_ARCH_MEMCPY */
>> > +
>> >         if (dest <= src) {
>> >                 tmp = dest;
>> >                 s = src;
>> > --
>> > 2.10.0
>> >
>>
>> Is there anything more that I have to do for this patch?
>>
>
> Probably a patch like this needs to go through Andrew.  Send it again
> and CC Andrew Morton <akpm@...ux-foundation.org>.  It would be nice if
> we could CC a better list than LKML but I don't know which one...  Few
> people read LKML.

I will add Andrew. Get maintainer script gave me a small list of email
id for this. I don't know if there is a better way than using
get_maintainer.pl.

> regards,
> dan carpenter

Thanks a lot for your time Dan.

Thanks,
PrasannaKumar