linux-kernel - Re: [PATCH v2 08/33] x86/intel_rdt: Add Class of service management

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Date:   Mon, 12 Sep 2016 11:02:04 -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>,
        Tejun Heo <tj@...nel.org>, Borislav Petkov <bp@...e.de>,
        Stephane Eranian <eranian@...gle.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Shaohua Li <shli@...com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Sai Prakhya <sai.praneeth.prakhya@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2 08/33] x86/intel_rdt: Add Class of service management

On 8 September 2016 at 04:57, Fenghua Yu <fenghua.yu@...el.com> wrote:
> diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
> index fcd0642..b25940a 100644
> --- a/arch/x86/kernel/cpu/intel_rdt.c
> +++ b/arch/x86/kernel/cpu/intel_rdt.c
> @@ -21,17 +21,94 @@
>   */
>  #include <linux/slab.h>
>  #include <linux/err.h>
> +#include <asm/intel_rdt.h>
> +
> +/*
> + * cctable maintains 1:1 mapping between CLOSid and cache bitmask.
> + */
> +static struct clos_cbm_table *cctable;
> +/*
> + * closid availability bit map.
> + */
> +unsigned long *closmap;
> +static DEFINE_MUTEX(rdtgroup_mutex);
> +
> +static inline void closid_get(u32 closid)
> +{
> +       struct clos_cbm_table *cct = &cctable[closid];
> +
> +       lockdep_assert_held(&rdtgroup_mutex);
> +
> +       cct->clos_refcnt++;
> +}
> +
> +static int closid_alloc(u32 *closid)
> +{
> +       u32 maxid;
> +       u32 id;
> +
> +       lockdep_assert_held(&rdtgroup_mutex);
> +
> +       maxid = boot_cpu_data.x86_cache_max_closid;
> +       id = find_first_zero_bit(closmap, maxid);
> +       if (id == maxid)
> +               return -ENOSPC;
> +
> +       set_bit(id, closmap);
> +       closid_get(id);
> +       *closid = id;
> +
> +       return 0;
> +}
> +
> +static inline void closid_free(u32 closid)
> +{
> +       clear_bit(closid, closmap);
> +       cctable[closid].cbm = 0;
> +}
> +
> +static void closid_put(u32 closid)
> +{
> +       struct clos_cbm_table *cct = &cctable[closid];
> +
> +       lockdep_assert_held(&rdtgroup_mutex);
> +       if (WARN_ON(!cct->clos_refcnt))
> +               return;
> +
> +       if (!--cct->clos_refcnt)
> +               closid_free(closid);
> +}
>

I would suggest a small change in the function names here.  I think
the names closid_free and closid_put should be swapped. As I
understand, under the current naming scheme, the opposite of
closid_alloc() is closid_put() and the opposite of closid_get() is
closid_free().  This is not the normal way these names are paired.
Typically, alloc and free go as a pair and get and put go as a pair.

--
Nilay