Re: [PATCH RFC V2 1/1] x86, perf: Add a freq pmu driver

Stephane Eranian
2015-07-21T03:10:14Z

On Mon, Jul 20, 2015 at 8:49 AM, Kan Liang <kan.liang@intel.com> wrote:
> From: Andy Lutomirski <luto@kernel.org>
>
> This patch adds freq PMU to support time and freq related counters
> includes TSC, IA32_APERF, IA32_MPERF and IA32_PPERF.
>
> The events are exposed in sysfs for use by perf stat and other tools.
> The files are under /sys/devices/freq/events/
>
> These events only support system-wide mode counting.
>
> The PMU type (attr->type) is PERF_TYPE_FREQ.
>
> Example:
>
> To caculate the CPU%
> CPU_Utilization = CPU_CLK_UNHALTED.REF_TSC / TSC
>
> $ perf stat -e '{ref-cycles,freq/tsc/}' -C0 -- taskset -c 0 sleep 1
> 3164023,,ref-cycles,1048387386,100.00
> 2410812089,,freq/tsc/,1050022373,100.00
> The CPU% for sleep is 0.13%.
>
This event is system-wide only. Thus, the kernel should return
an error when you try to use it in per-thread mode. That would
be more consistent with RAPL and uncore events.

> $ perf stat -e '{ref-cycles,freq/tsc/}' -C0 -- taskset -c 0 busyloop
> 15662183572,,ref-cycles,6822637855,100.00
> 15667608992,,freq/tsc/,6823978523,100.00
> The CPU% for busy loop is 99.9%.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Kan Liang <kan.liang@intel.com>
> ---
>
> The patch is based on the patch "x86, perf: Add an aperfmperf driver"
> from Andy Lutomirski (https://lkml.org/lkml/2015/4/28/757)
>
> Changes from V1
> - Change the name from aperfmperf to freq
> - Add TSC and PPERF support
> - Change to perf_sw_context
> - Assign new PERF_TYPE name
> - Split stop_or_del to two functions
> - Update state of hw_perf_event
> - Update changlog
>
> arch/x86/kernel/cpu/Makefile | 2 +
> arch/x86/kernel/cpu/perf_event_freq.c | 207 ++++++++++++++++++++++++++++++++++
> include/uapi/linux/perf_event.h | 1 +
> 3 files changed, 210 insertions(+)
> create mode 100644 arch/x86/kernel/cpu/perf_event_freq.c
>
> diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
> index 9bff687..f621dba 100644
> --- a/arch/x86/kernel/cpu/Makefile
> +++ b/arch/x86/kernel/cpu/Makefile
> @@ -46,6 +46,8 @@ obj-$(CONFIG_PERF_EVENTS_INTEL_UNCORE) += perf_event_intel_uncore.o \
> perf_event_intel_uncore_snb.o \
> perf_event_intel_uncore_snbep.o \
> perf_event_intel_uncore_nhmex.o
> +obj-$(CONFIG_CPU_SUP_INTEL) += perf_event_freq.o
> +obj-$(CONFIG_CPU_SUP_AMD) += perf_event_freq.o
> endif
>
>
> diff --git a/arch/x86/kernel/cpu/perf_event_freq.c b/arch/x86/kernel/cpu/perf_event_freq.c
> new file mode 100644
> index 0000000..9389b3b
> --- /dev/null
> +++ b/arch/x86/kernel/cpu/perf_event_freq.c
> @@ -0,0 +1,207 @@
> +#include <linux/perf_event.h>
> +
> +enum perf_freq_id {
> + /*
> + * freq events, generalized by the kernel:
> + */
> + PERF_FREQ_TSC = 0,
> + PERF_FREQ_APERF = 1,
> + PERF_FREQ_MPERF = 2,
> + PERF_FREQ_PPERF = 3,
> +
> + PERF_FREQ_EVENT_MAX, /* non-ABI */
> +};
> +
> +struct perf_freq_msr {
> + int id;
> + u64 msr;
> +};
> +
> +static struct perf_freq_msr freq_msr[] = {
> + { PERF_FREQ_TSC, 0 },
> + { PERF_FREQ_APERF, MSR_IA32_APERF },
> + { PERF_FREQ_MPERF, MSR_IA32_MPERF },
> + { PERF_FREQ_PPERF, MSR_PPERF },
> +};
> +
> +
> +
> +PMU_EVENT_ATTR_STRING(tsc, evattr_tsc, "event=0x00");
> +PMU_EVENT_ATTR_STRING(aperf, evattr_aperf, "event=0x01");
> +PMU_EVENT_ATTR_STRING(mperf, evattr_mperf, "event=0x02");
> +PMU_EVENT_ATTR_STRING(pperf, evattr_pperf, "event=0x03");
> +
> +static struct attribute *events_attrs[PERF_FREQ_EVENT_MAX + 1] = {
> + &evattr_tsc.attr.attr,
> +};
> +
> +static struct attribute_group events_attr_group = {
> + .name = "events",
> + .attrs = events_attrs,
> +};
> +
> +PMU_FORMAT_ATTR(event, "config:0-63");
> +static struct attribute *format_attrs[] = {
> + &format_attr_event.attr,
> + NULL,
> +};
> +static struct attribute_group format_attr_group = {
> + .name = "format",
> + .attrs = format_attrs,
> +};
> +
> +static const struct attribute_group *attr_groups[] = {
> + &events_attr_group,
> + &format_attr_group,
> + NULL,
> +};
> +
> +static int freq_event_init(struct perf_event *event)
> +{
> + u64 cfg = event->attr.config;
> +
> + if (event->attr.type != event->pmu->type)
> + return -ENOENT;
> +
> + if (cfg >= PERF_FREQ_EVENT_MAX)
> + return -EINVAL;
> +
> + /* unsupported modes and filters */
> + if (event->attr.exclude_user ||
> + event->attr.exclude_kernel ||
> + event->attr.exclude_hv ||
> + event->attr.exclude_idle ||
> + event->attr.exclude_host ||
> + event->attr.exclude_guest ||
> + event->attr.sample_period) /* no sampling */
> + return -EINVAL;
> +
> + event->hw.idx = -1;
> + event->hw.event_base = freq_msr[cfg].msr;
> + event->hw.config = cfg;
> +
> + return 0;
> +}
> +
> +static inline u64 freq_read_counter(struct perf_event *event)
> +{
> + u64 now;
> +
> + if (event->hw.event_base)
> + rdmsrl(event->hw.event_base, now);
> + else
> + now = rdtsc();
> +
> + return now;
> +}
> +static void freq_event_update(struct perf_event *event)
> +{
> + u64 prev;
> + u64 now;
> +
> + /* Assume counters are 64bit */
> + now = freq_read_counter(event);
> + prev = local64_xchg(&event->hw.prev_count, now);
> + local64_add(now - prev, &event->count);
> +}
> +
> +static void freq_event_start(struct perf_event *event, int flags)
> +{
> + u64 now;
> +
> + now = freq_read_counter(event);
> + local64_set(&event->hw.prev_count, now);
> +}
> +
> +static void freq_event_stop(struct perf_event *event, int flags)
> +{
> + struct hw_perf_event *hwc = &event->hw;
> +
> + /* mark event as deactivated and stopped */
> + if (!(hwc->state & PERF_HES_STOPPED))
> + hwc->state |= PERF_HES_STOPPED;
> +
> + /* check if update of sw counter is necessary */
> + if ((flags & PERF_EF_UPDATE) && !(hwc->state & PERF_HES_UPTODATE)) {
> + freq_event_update(event);
> + hwc->state |= PERF_HES_UPTODATE;
> + }
> +}
> +
> +static void freq_event_del(struct perf_event *event, int flags)
> +{
> + freq_event_stop(event, PERF_EF_UPDATE);
> +}
> +
> +static int freq_event_add(struct perf_event *event, int flags)
> +{
> + struct hw_perf_event *hwc = &event->hw;
> +
> + hwc->state = PERF_HES_UPTODATE | PERF_HES_STOPPED;
> +
> + if (flags & PERF_EF_START)
> + freq_event_start(event, flags);
> +
> + return 0;
> +}
> +
> +static struct pmu pmu_freq = {
> + .task_ctx_nr = perf_sw_context,
> + .attr_groups = attr_groups,
> + .event_init = freq_event_init,
> + .add = freq_event_add,
> + .del = freq_event_del,
> + .start = freq_event_start,
> + .stop = freq_event_stop,
> + .read = freq_event_update,
> + .capabilities = PERF_PMU_CAP_NO_INTERRUPT,
> +};
> +
> +static int __init intel_freq_specific_init(int idx)
> +{
> + /* Skylake has pperf support */
> + if ((boot_cpu_data.x86_model == 78) ||
> + (boot_cpu_data.x86_model == 94))
> + events_attrs[idx++] = &evattr_pperf.attr.attr;
> +
> + events_attrs[idx++] = NULL;
> +
> + return 0;
> +}
> +
> +static int __init amd_freq_specific_init(int idx)
> +{
> + return 0;
> +}
> +
> +static int __init freq_init(void)
> +{
> + int err;
> + int idx = 1;
> +
> + if (boot_cpu_has(X86_FEATURE_APERFMPERF)) {
> + events_attrs[idx++] = &evattr_aperf.attr.attr;
> + events_attrs[idx++] = &evattr_mperf.attr.attr;
> + }
> +
> + switch (boot_cpu_data.x86_vendor) {
> + case X86_VENDOR_INTEL:
> + err = intel_freq_specific_init(idx);
> + break;
> + case X86_VENDOR_AMD:
> + err = amd_freq_specific_init(idx);
> + break;
> + default:
> + err = -ENOTSUPP;
> + }
> +
> + if (err != 0) {
> + pr_cont("no freq PMU driver.\n");
> + return 0;
> + }
> +
> + perf_pmu_register(&pmu_freq, "freq", PERF_TYPE_FREQ);
> +
> + return 0;
> +}
> +device_initcall(freq_init);
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index d97f84c..1f8c400 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -32,6 +32,7 @@ enum perf_type_id {
> PERF_TYPE_HW_CACHE = 3,
> PERF_TYPE_RAW = 4,
> PERF_TYPE_BREAKPOINT = 5,
> + PERF_TYPE_FREQ = 6,
>
What's the point of this when we can dynamically register a PMU?
There has not been anymore modification to perf_type_id since a very long
time ago. Not sure why this proposal qualifies for that?
The perf tool can find the PMU type from sysfs.

> PERF_TYPE_MAX, /* non-ABI */
> };
> --
> 1.8.3.1
>