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Subject: Re: [PATCH 0/4] Reinstate and improve MIPS `do_div' implementation
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From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <2d636696-35f0-4731-b1c3-5445a57964fb@www.fastmail.com>
Date:   Thu, 22 Apr 2021 18:00:55 +0200
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Huacai Chen <chenhuacai@kernel.org>,
        Huacai Chen <chenhuacai@loongson.cn>,
        linux-arch@vger.kernel.org,
        "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Paul Boddie <paul@boddie.org.uk>,
        Lubomir Rintel <lkundrak@v3.sk>
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Message-Id: <895956F9-4EBC-4C8A-9BF2-7E457E96C1D7@goldelico.com>
References: <alpine.DEB.2.21.2104200044060.44318@angie.orcam.me.uk> <51BC7C74-68BF-4A8E-8CFB-DB4EBBC89706@goldelico.com> <alpine.DEB.2.21.2104211904490.44318@angie.orcam.me.uk> <E6326E8A-50DA-4F81-9865-F29EE0E298A9@goldelico.com> <2d636696-35f0-4731-b1c3-5445a57964fb@www.fastmail.com>
To:     Jiaxun Yang <jiaxun.yang@flygoat.com>,
        "Maciej W. Rozycki" <macro@orcam.me.uk>
Precedence: bulk

Hi,

> Am 22.04.2021 um 15:39 schrieb Jiaxun Yang <jiaxun.yang@flygoat.com>:
>=20
>=20
>=20
> On Thu, Apr 22, 2021, at 1:53 PM, H. Nikolaus Schaller wrote:
>> Hi,
>>=20
>>> Am 21.04.2021 um 21:04 schrieb Maciej W. Rozycki =
<macro@orcam.me.uk>:
>>>=20
>>> On Wed, 21 Apr 2021, H. Nikolaus Schaller wrote:
>>>=20
>>>>> In the end I have included four patches on this occasion: 1/4 is =
the test=20
>>>>> module, 2/4 is an inline documentation fix/clarification for the =
`do_div'=20
>>>>> wrapper, 3/4 enables the MIPS `__div64_32' backend and 4/4 adds a =
small=20
>>>>> performance improvement to it.
>>>>=20
>>>> How can I apply them to the kernel? There is something wrong which =
makes
>>>> git am fail.
>>>=20
>>> I don't know.  The changes were made against vanilla 5.12-rc7, but =
then=20
>>> the pieces affected have not changed for ages.  FWIW I can `git am' =
the=20
>>> series as received back just fine.
>>=20
>> Please can you point me to some download/pull/gitweb? It seems as if =
the series
>> also did not appear at =
https://patchwork.kernel.org/project/linux-mips/list/
>>=20
>=20
> You may try download raw from:
>=20
> =
https://lore.kernel.org/linux-mips/E6326E8A-50DA-4F81-9865-F29EE0E298A9@go=
ldelico.com/T/#t

I simply tried again and it seems that I had tried to git am it on top =
of the
patches from Huacai which of course fails.

Now I could run the tests:

from [PATCH 4/4]:

> This has passed correctness verification with test_div64 and reduced =
the
> module's average execution time down to 1.0445s and 0.2619s from =
1.0668s
> and 0.2629s respectively for an R3400 CPU @40MHz and a 5Kc CPU =
@160MHz.

test only [PATCH 1/4 and 2/4]:

[  256.301140] test_div64: Completed 64bit/32bit division and modulo =
test, 0.291154944s elapsed

+ [PATCH 3/4]

[ 1698.698920] test_div64: Completed 64bit/32bit division and modulo =
test, 0.132142865s elapsed

+ [PATCH 4/4]

[  466.818349] test_div64: Completed 64bit/32bit division and modulo =
test, 0.134429075s elapsed

So the new code is indeed faster than the default implementation.
[PATCH 4/4] has no significant influence (wouldn't say it is slower =
because timer resolution
isn't very high on this machine and the kernel has some scheduling issue =
[1]).

Anyways the JZ4730 can boot and works with these patches included.

BR and thanks,
Nikolaus Schaller


[1] we are preparing full support for the JZ4730 based Skytone Alpha =
machine. Most features
are working except sound/I2S. I2C is a little unreliable and Ethernet =
has hickups. And scheduling
which indicates some fundamental IRQ or timer issue we could not yet =
identify.

So if anyone happens to have such a machine and can help debugging, =
please contact me.