linux-kernel - Re: [PATCH v4 2/5] LoongArch: Use la.pcrel instead of la.abs for exception handlers

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Message-ID: <848e2985-9ba3-c14d-23ac-a7f1c218215f@loongson.cn>
Date:   Thu, 16 Feb 2023 10:32:48 +0800
From:   Youling Tang <tangyouling@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>, Xi Ruoyao <xry111@...111.site>
Cc:     Jinyang He <hejinyang@...ngson.cn>,
        Xuerui Wang <kernel@...0n.name>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
        Jianmin lv <lvjianmin@...ngson.cn>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>
Subject: Re: [PATCH v4 2/5] LoongArch: Use la.pcrel instead of la.abs for
 exception handlers

Hi folks,

On 02/10/2023 05:18 PM, Youling Tang wrote:
>
>
> On 02/10/2023 05:09 PM, Huacai Chen wrote:
>> Hi, Youling and Ruoyao,
>>
>> Thank you very much for implementing the per-node exceptions. But I
>> want to know if the per-node solution is really worthy for a PIE
>> kernel. So, could you please test the performance? Maybe we can reduce
>> the complexity if we give up the per-node solution.

Tested on Loongson-3C5000L-LL machine, using CLFS7.3 system.

- nopernode:
   Based on the v1 patch method, and remove the else branch process in
   setup_tlb_handler().

- pernode: Based on the v4 patch method.

- pie: Enable RANDOMIZE_BASE (KASLR).

- nopie: Disable RANDOMIZE_BASE and RELOCATABLE.


The UnixBench test results are as follows:

- nopernode-nopie: 3938.7

- pernode-nopie: 4062.2

- nopernode-pie: 4009.7

- pernode-pie: 4028.7

In general, `pernode` is higher than `nopernode`, and `nopie` is higher
than `pie`. (except that nopernode-pie is higher than nopernode-nopie,
which is not as expected, which may be caused by the instability of the
machine).

Everyone is more inclined to use `pernode` or `nopernode` to implement
in the exception handling process?

Youling.