linux-kernel - Re: [PATCH v3 01/18] Documentation, ABI: Add a document entry for cache id

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Date:   Sat, 8 Oct 2016 12:11:08 -0500
From:   Nilay Vaish <nilayvaish@...il.com>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>, Shaohua Li <shli@...com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Sai Prakhya <sai.praneeth.prakhya@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v3 01/18] Documentation, ABI: Add a document entry for
 cache id

On 7 October 2016 at 21:45, Fenghua Yu <fenghua.yu@...el.com> wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
>
> Add an ABI document entry for /sys/devices/system/cpu/cpu*/cache/index*/id.
>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  Documentation/ABI/testing/sysfs-devices-system-cpu | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index 4987417..b1c3d69 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -272,6 +272,22 @@ Description:       Parameters for the CPU cache attributes
>                                      the modified cache line is written to main
>                                      memory only when it is replaced
>
> +
> +What:          /sys/devices/system/cpu/cpu*/cache/index*/id
> +Date:          September 2016
> +Contact:       Linux kernel mailing list <linux-kernel@...r.kernel.org>
> +Description:   Cache id
> +
> +               The id provides a unique name for a specific instance of
> +               a cache of a particular type. E.g. there may be a level
> +               3 unified cache on each socket in a server and we may
> +               assign them ids 0, 1, 2, ...
> +
> +               Note that id value may not be contiguous. E.g. level 1
> +               caches typically exist per core, but there may not be a
> +               power of two cores on a socket, so these caches may be
> +               numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ...
> +

While it is ok that the caches are not numbered contiguously, it is
unclear how this is related to number of cores on a socket being a
power of 2 or not.

--
Nilay