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    SubjectRe: [PATCH v5 12/20] x86: perf: intel_pt: Intel PT PMU driver
    Date
    Peter Zijlstra <peterz@infradead.org> writes:

    > On Mon, Oct 13, 2014 at 04:45:40PM +0300, Alexander Shishkin wrote:
    >> +
    >> +enum cpuid_regs {
    >> + CR_EAX = 0,
    >> + CR_ECX,
    >> + CR_EDX,
    >> + CR_EBX
    >> +};
    >> +
    >> +/*
    >> + * Capabilities of Intel PT hardware, such as number of address bits or
    >> + * supported output schemes, are cached and exported to userspace as "caps"
    >> + * attribute group of pt pmu device
    >> + * (/sys/bus/event_source/devices/intel_pt/caps/) so that userspace can store
    >> + * relevant bits together with intel_pt traces.
    >> + */
    >> +#define PT_CAP(_n, _l, _r, _m) \
    >> + [PT_CAP_ ## _n] = { .name = __stringify(_n), .leaf = _l, \
    >> + .reg = _r, .mask = _m }
    >> +
    >> +static struct pt_cap_desc {
    >> + const char *name;
    >> + u32 leaf;
    >> + u8 reg;
    >> + u32 mask;
    >> +} pt_caps[] = {
    >> + PT_CAP(max_subleaf, 0, CR_EAX, 0xffffffff),
    >> + PT_CAP(cr3_filtering, 0, CR_EBX, BIT(0)),
    >> + PT_CAP(topa_output, 0, CR_ECX, BIT(0)),
    >> + PT_CAP(topa_multiple_entries, 0, CR_ECX, BIT(1)),
    >> + PT_CAP(payloads_lip, 0, CR_ECX, BIT(31)),
    >> +};
    >> +
    >> +static u32 pt_cap_get(enum pt_capabilities cap)
    >> +{
    >> + struct pt_cap_desc *cd = &pt_caps[cap];
    >> + u32 c = pt_pmu.caps[cd->leaf * 4 + cd->reg];
    >> + unsigned int shift = __ffs(cd->mask);
    >> +
    >> + return (c & cd->mask) >> shift;
    >> +}
    >
    >> + if (test_cpu_cap(&boot_cpu_data, X86_FEATURE_INTEL_PT)) {
    >> + for (i = 0; i < PT_CPUID_LEAVES; i++)
    >> + cpuid_count(20, i,
    >> + &pt_pmu.caps[CR_EAX + i * 4],
    >> + &pt_pmu.caps[CR_EBX + i * 4],
    >> + &pt_pmu.caps[CR_ECX + i * 4],
    >> + &pt_pmu.caps[CR_EDX + i * 4]);
    >> + } else
    >> + return -ENODEV;
    >
    > I would really rather you use bitfield unions for cpuid stuff, have a
    > look at union cpuid10_e[abd]x as used in
    > perf_event_intel.c:intel_pmu_init().

    It looks like it would only work for the first cpuid leaf, but we'll
    need more than that. And the array makes it easier to allocate
    attributes for sysfs en masse.

    I guess it doesn't really matter if we use unions unless these bits need
    to be exported to other parts of the kernel? But *that* is hardly a good
    idea. What do you think?

    Regards,
    --
    Alex


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