linux-kernel - Re: [PATCH v4 4/4] Documentation/admin-guide: Change doc for split_lock

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Date:   Wed, 27 Jan 2021 23:09:38 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v4 4/4] Documentation/admin-guide: Change doc for split_lock_detect parameter

On Tue, Nov 24 2020 at 20:52, Fenghua Yu wrote:
> Since #DB for bus lock detect changes the split_lock_detect parameter,
> update the documentation for the changes.

Why is this seperate and an all in one thing? patch 2/4 changes the
parameter first and 3/4 adds a new option....

>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> Acked-by: Randy Dunlap <rdunlap@...radead.org>
> ---
> Change Log:
> v4:
> - Fix a ratelimit wording issue in the doc (Randy).
> - Patch 4 is acked by Randy (Randy).
>
> v3:
> - Enable Bus Lock Detection when fatal to handle bus lock from non-WB
>   (PeterZ).
>
> v1:
> - Fix a few wording issues (Randy).
>
> RFC v2:
> - Simplify the documentation (Randy).
>
>  .../admin-guide/kernel-parameters.txt         | 30 +++++++++++++++----
>  1 file changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 44fde25bb221..28228539b02a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5051,27 +5051,45 @@
>  	spia_peddr=
> +
> +			ratelimit:N -
> +				  Set rate limit to N bus locks per second
> +				  for bus lock detection. 0 < N <= HZ/2.

Oh well. So if I have ratelimit:500 on the kernel command line and then
this works for CONFIG_HZ=1000, but after rebuilding the kernel with
HZ=250 it fails. What?

If I allow 500 hits per second then CONFIG_HZ has absolutely nothing to
do with it. A second stays a second independent of CONFIG_HZ.

So what's the purpose of this HZ business?

Thanks,

        tglx