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

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Date:   Thu, 16 Feb 2023 14:56:20 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Youling Tang <tangyouling@...ngson.cn>
Cc:     Xi Ruoyao <xry111@...111.site>, 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

On Thu, Feb 16, 2023 at 10:32 AM Youling Tang <tangyouling@...ngson.cn> wrote:
>
> 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?
>From my point of view, for the PIE kernel the performance difference
between pernode and nopoernode is negligible. On the other hand,
pernode implementation needs some compiler hackings and makes the
logic significantly complex. So I prefer to remove the pernode
exception support.

Huacai
>
> Youling.
>
>