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    SubjectRe: [PATCH 4/8] x86/intel_rct/mba: Add MBA structures and initialize MBA
    On Fri, 17 Feb 2017, Vikas Shivappa wrote:
    > --- a/arch/x86/include/asm/intel_rdt.h
    > +++ b/arch/x86/include/asm/intel_rdt.h
    > @@ -11,6 +11,9 @@
    > #define IA32_L3_QOS_CFG 0xc81
    > #define IA32_L3_CBM_BASE 0xc90
    > #define IA32_L2_CBM_BASE 0xd10
    > +#define IA32_MBA_THRTL_BASE 0xd50
    > +#define MAX_MBA_THRTL 100u
    > +#define MBA_IS_LINEAR 0x4

    I have a hard time to figure out how the latter two constants are related
    to this list of registers. MBA_IS_LINEAR is used to check the CPUID bit and
    MAX_MBA_THRTL is obviously a pure software constant because with a
    non-linear scale the maximum value is not 100.

    Just slapping defines to random places is equally bad as using hard coded
    constants.

    > +/*
    > + * rdt_get_mb_table() - get a mapping of b/w percentage values
    > + * exposed to user interface and the h/w understandable delay values.
    > + *
    > + * The non-linear delay values have the granularity of power of two
    > + * and also the h/w does not guarantee a curve for configured delay
    > + * values vs. actual b/w throttled.
    > + * Hence we need a mapping that is pre caliberated for user to express
    > + * the b/w in terms of any sensible number.

    ... calibrated so the user can express the bandwidth as a percentage value.

    > +static inline int rdt_get_mb_table(struct rdt_resource *r)
    > +{
    > + /*
    > + * There are no Intel SKUs as of now to support non-linear delay.
    > + */
    > + r->mb_map = NULL;

    What's the point of setting this to NULL?

    Also it would be helpful to emit log info here so people don't have to
    start digging around.

    pr_info("Bandwidth map not implemented for ....", ... model);

    > +
    > + return -ENODEV;

    Returning -ENODEV to a function which just returns a boolean value is
    pointless.

    > static void rdt_get_cache_config(int idx, struct rdt_resource *r)
    > {
    > union cpuid_0x10_1_eax eax;
    > @@ -184,9 +237,8 @@ static inline bool get_rdt_resources(void)
    > ret = true;
    > }
    >
    > - if (boot_cpu_has(X86_FEATURE_MBA)) {
    > - ret = true;
    > - }
    > + if (boot_cpu_has(X86_FEATURE_MBA))
    > + ret = rdt_get_mem_config(&rdt_resources_all[RDT_RESOURCE_MBA]);

    Groan. When rdt_get_mem_config() returns false (because the map is not
    implemented), then the whole function returns false and CAT is disabled.

    > +static int domain_setup_ctrlval(struct rdt_resource *r, struct rdt_domain *d)
    > +{
    > + int i;
    > +
    > + d->ctrl_val = kmalloc_array(r->num_closid,
    > + sizeof(*d->ctrl_val), GFP_KERNEL);
    > + if (!d->ctrl_val)
    > + return -ENOMEM;
    > +
    > + /*
    > + * Initialize the Control MSRs to having no control.
    > + * For Cache Allocation: Set all bits in cbm
    > + * For Memory Allocation: Set b/w requested to 100
    > + */
    > + for (i = 0; i < r->num_closid; i++) {
    > + int idx = cbm_idx(r, i);
    > +
    > + d->ctrl_val[i] = r->default_ctrl;
    > + wrmsrl(r->msr_base + idx, d->ctrl_val[i]);
    > + }

    So if you use a local pointer for that, this whole mess becomes readable.

    static int domain_setup_ctrlval(struct rdt_resource *r, struct rdt_domain *d)
    {
    u32 *p;
    int i;

    p = kmalloc_array(r->num_closid, sizeof(*d->ctrl_val), GFP_KERNEL);
    if (!p)
    return -ENOMEM;

    d->ctrl_val = p;

    /* Initialize the Control MSRs to the default value */
    for (i = 0; i < r->num_closid; i++, p++) {
    int idx = cbm_idx(r, i);

    *p = r->default_ctrl;
    wrmsrl(r->msr_base + idx, *p);
    }
    > +
    > + return 0;
    > +}

    > static void domain_add_cpu(int cpu, struct rdt_resource *r)
    > {
    > - int i, id = get_cache_id(cpu, r->cache_level);
    > + int id = get_cache_id(cpu, r->cache_level), ret;
    Bah. If you have the same type in one line, then please move the
    uninitialized variables to the front.

    int ret, id = get_cache_id(cpu, r->cache_level);

    But a s/i/ret/ would have been to simple and kept the code readable.

    > @@ -298,19 +374,12 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
    >
    > d->id = id;
    >
    > - d->ctrl_val = kmalloc_array(r->num_closid, sizeof(*d->ctrl_val), GFP_KERNEL);
    > - if (!d->ctrl_val) {
    > + ret = domain_setup_ctrlval(r, d);
    > + if (ret) {
    > kfree(d);
    > return;
    > }

    What's the point of this 'ret' variable if the function is void?

    if (domain_setup_ctrlval(r, d)) {
    kfree(d);
    return;
    }
    would have been to easy to read, right?

    Thanks,

    tglx

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