Re: [PATCH 1/2] mips: convert syscall to generic entry

From: Zhou Yanjie <zhouyu@wanyeetech.com>
To: "Jiaxun Yang" <jiaxun.yang@flygoat.com>,
	"Thomas Bogendoerfer" <tsbogend@alpha.franken.de>,
	陈飞扬 <chris.chenfeiyang@gmail.com>,
	"Paul Cercueil" <paul@crapouillou.net>,
	"H. Nikolaus Schaller" <hns@goldelico.com>
Cc: tglx@linutronix.de, peterz@infradead.org, luto@kernel.org,
	arnd@arndb.de, Feiyang Chen <chenfeiyang@loongson.cn>,
	linux-mips@vger.kernel.org, linux-arch@vger.kernel.org,
	chenhuacai@kernel.org, Yanteng Si <siyanteng@loongson.cn>
Subject: Re: [PATCH 1/2] mips: convert syscall to generic entry
Date: Thu, 9 Sep 2021 20:45:25 +0800	[thread overview]
Message-ID: <7e2c0db1-bf5a-8f16-bc43-81830a30045e@wanyeetech.com> (raw)
In-Reply-To: <13d237ab-0ef3-772d-6f21-ff023781efcf@flygoat.com>

Hi,

On 2021/9/8 下午8:41, Jiaxun Yang wrote:
>
> 在 2021/9/8 16:51, Thomas Bogendoerfer 写道:
>> On Wed, Sep 08, 2021 at 10:08:47AM +0800, 陈飞扬 wrote:
>>> On Tue, 7 Sept 2021 at 21:49, Jiaxun Yang <jiaxun.yang@flygoat.com> 
>>> wrote:
>>>>
>>>> 在 2021/9/7 14:16, FreeFlyingSheep 写道:
>>>>> From: Feiyang Chen <chenfeiyang@loongson.cn>
>>>>>
>>>>> Convert mips syscall to use the generic entry infrastructure from
>>>>> kernel/entry/*.
>>>>>
>>>>> There are a few special things on mips:
>>>>>
>>>>> - There is one type of syscall on mips32 (scall32-o32) and three 
>>>>> types
>>>>> of syscalls on mips64 (scall64-o32, scall64-n32 and scall64-n64). Now
>>>>> convert to C code to handle different types of syscalls.
>>>>>
>>>>> - For some special syscalls (e.g. fork, clone, clone3 and sysmips),
>>>>> save_static_function() wrapper is used to save static registers. Now
>>>>> SAVE_STATIC is used in handle_sys before calling do_syscall(), so the
>>>>> save_static_function() wrapper can be removed.
>>>>>
>>>>> - For sigreturn/rt_sigreturn and sysmips, inline assembly is used to
>>>>> jump to syscall_exit directly for skipping setting the error flag and
>>>>> restoring all registers. Now use regs->regs[27] to mark whether to
>>>>> handle the error flag and always restore all registers in handle_sys,
>>>>> so these functions can return normally as other architecture.
>>>> Hmm, that would give us overhead of register context on these 
>>>> syscalls.
>>>>
>>>> I guess it's worthy?
>>>>
>>> Hi, Jiaxun,
>>>
>>> Saving and restoring registers against different system calls can be
>>> difficult due to the use of generic entry.
>>> To avoid a lot of duplicate code, I think the overhead is worth it.
>> could you please provide numbers for that ? This code still runs
>> on low end MIPS CPUs for which overhead might mean a different
>> ballpark than some highend Loongson CPUs.
>
> It shows ~3% regression for UnixBench on MT7621A (1004Kec).
>
> + Yanjie could you help with a run on ingenic platform?

Sure, I can help with JZ4775, JZ4780, X1000, X1830, X2000 from Ingenic, 
and SF16A18, SF19A2890 from SiFlower.

+ Paul could you help with a run on JZ4760 and JZ4770?

+ Nikolaus could you help with a run on JZ4730?

Thanks and best regards!

>
> Thanks.
>
> - Jiaxun
>
>>
>> Thomas.
>>