linux-kernel - Re: [PATCH] tools/power/x86/turbostat: Fix TCC offset bit mask

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Message-ID: <CAJvTdKm3h_msmu-NjTPY+09bLqyVL_-GCHnGFdNGdTcSZRP4zQ@mail.gmail.com>
Date:   Thu, 11 Mar 2021 18:18:53 -0500
From:   Len Brown <lenb@...nel.org>
To:     Doug Smythies <doug.smythies@...il.com>
Cc:     Doug Smythies <dsmythies@...us.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] tools/power/x86/turbostat: Fix TCC offset bit mask

Thanks for the close read, Doug.

This field size actually varies from system to system,
but the reality is that the offset is never that big, and so the
smaller mask is sufficient.

Finally, this may all be moot, because there is discussion that using
the offset this way is simply erroneous.  stay tuned.

-Len


On Sat, Jan 16, 2021 at 12:07 PM Doug Smythies <doug.smythies@...il.com> wrote:
>
> The TCC offset mask is incorrect, resulting in
> incorrect target temperature calculations, if
> the offset is big enough to exceed the mask size.
>
> Signed-off-by: Doug Smythies <dsmythies@...us.net>
> ---
>  tools/power/x86/turbostat/turbostat.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
> index 389ea5209a83..d7acdd4d16c4 100644
> --- a/tools/power/x86/turbostat/turbostat.c
> +++ b/tools/power/x86/turbostat/turbostat.c
> @@ -4823,7 +4823,7 @@ int read_tcc_activation_temp()
>
>         target_c = (msr >> 16) & 0xFF;
>
> -       offset_c = (msr >> 24) & 0xF;
> +       offset_c = (msr >> 24) & 0x3F;
>
>         tcc = target_c - offset_c;
>
> --
> 2.25.1
>


-- 
Len Brown, Intel Open Source Technology Center