linux-kernel - Re: [PATCH 0/4] Reinstate and improve MIPS `do

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Date:   Thu, 22 Apr 2021 18:00:55 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>,
        "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhuacai@...nel.org>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        linux-arch@...r.kernel.org,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Boddie <paul@...die.org.uk>,
        Lubomir Rintel <lkundrak@...sk>
Subject: Re: [PATCH 0/4] Reinstate and improve MIPS `do_div' implementation

Hi,

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