linux-kernel - Re: [PATCH 2/2][v2] x86/resctrl: Add task resctrl information display

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Message-ID: <20191118144807.GE6363@zn.tnic>
Date:   Mon, 18 Nov 2019 15:48:07 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ryan Chen <yu.chen.surf@...il.com>
Cc:     Chen Yu <yu.c.chen@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        Kees Cook <keescook@...omium.org>,
        Christian Brauner <christian@...uner.io>,
        Shakeel Butt <shakeelb@...gle.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/2][v2] x86/resctrl: Add task resctrl information display

On Sat, Nov 16, 2019 at 11:01:12PM +0800, Ryan Chen wrote:
> Right, we can return 'blank' to user and let the user to parse the information.

There is nothing to parse - the task doesn't belong to any groups. That's it.

> And there is a similar behavior in cgroup that, for kernel thread that
> does not belong
> to any cgroup, /proc/{pid}/cgroup just show 'blank' without returning an error.

By 'blank' I assume you mean the empty string '' ?

> Yes, only when PROC_FS is set, /proc/{pid}/resctrl
> can be displayed. However, CPU_RESCTRL might not
> depend on proc fs, it is possible that the CPU_RESCTRL
> is enabled but without PROC_FS set. If I understand correctly,
>  CPU_RESCTRL is the 'root' config for X86_CPU_RESCTRL,
> after reading this thread:
> https://lists.gt.net/linux/kernel/3211659

I'm not sure I know what you mean here. There's no CPU_RESCTRL option - you've
added it in the previous patch:

[ ~/kernel/linux> git grep -E CONFIG_CPU_RESCTRL
[ ~/kernel/linux> git grep -E "\WCPU_RESCTRL"
[ ~/kernel/linux>

And if you want to use that option in proc/, then it needs
to depend on PROC_FS, like the the example I gave you with
CONFIG_PROC_PID_ARCH_STATUS.

Or do you mean something else?

>  If this is the case, shall we add the new file at kernel/resctrl/resctrl.c?
> And the generic proc_resctrl_show() could be put into this file. In the future
> the generic code for resctrl could be added/moved to kernel/resctrl/resctrl.c

Not worth it for a single function. Leave it in
arch/x86/kernel/cpu/resctrl/rdtgroup.c where you had it.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette