linux-kernel - Re: [PATCH 08/10] x86, perf: Support sysfs files depending on SMT status

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Date:	Wed, 16 Dec 2015 04:48:52 -0800
From:	Stephane Eranian <eranian@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 08/10] x86, perf: Support sysfs files depending on SMT status

Andi,

On Tue, Dec 15, 2015 at 4:54 PM, Andi Kleen <andi@...stfloor.org> wrote:
>
> From: Andi Kleen <ak@...ux.intel.com>
>
> Add a way to show different sysfs events attributes depending on
> HyperThreading is on or off. This is difficult to determine
> early at boot, so we just do it dynamically when the sysfs
> attribute is read.
>
The only attribute I can think of is the any thread bit.
But I do not see this in this patch. Is this somewhere else?

>
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/kernel/cpu/perf_event.c | 34 ++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/cpu/perf_event.h | 10 ++++++++++
>  include/linux/perf_event.h       |  7 +++++++
>  3 files changed, 51 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 9dfbba5..976686f 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -1590,6 +1590,40 @@ ssize_t events_sysfs_show(struct device *dev, struct device_attribute *attr,
>         return x86_pmu.events_sysfs_show(page, config);
>  }
>
> +ssize_t events_ht_sysfs_show(struct device *dev, struct device_attribute *attr,
> +                         char *page)
> +{
> +       struct perf_pmu_events_ht_attr *pmu_attr =
> +               container_of(attr, struct perf_pmu_events_ht_attr, attr);
> +       bool ht_on = false;
> +       int cpu;
> +
> +       /*
> +        * Report conditional events depending on Hyper-Threading.
> +        *
> +        * Check all online CPUs if any have a thread sibling,
> +        * as perf may measure any of them.
> +        *
> +        * This is overly conservative as usually the HT special
> +        * handling is not needed if the other CPU thread is idle.
> +        *
> +        * Note this does not (cannot) handle the case when thread
> +        * siblings are invisible, for example with virtualization
> +        * if they are owned by some other guest.  The user tool
> +        * has to re-read when a thread sibling gets onlined later.
> +        */
> +       for_each_online_cpu (cpu) {
> +               ht_on = cpumask_weight(topology_sibling_cpumask(cpu)) > 1;
> +               if (ht_on)
> +                       break;
> +       }
> +
> +       return sprintf(page, "%s",
> +                       ht_on ?
> +                       pmu_attr->event_str_ht :
> +                       pmu_attr->event_str_noht);
> +}
> +
>  EVENT_ATTR(cpu-cycles,                 CPU_CYCLES              );
>  EVENT_ATTR(instructions,               INSTRUCTIONS            );
>  EVENT_ATTR(cache-references,           CACHE_REFERENCES        );
> diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
> index 799e6bd..ce87cd6 100644
> --- a/arch/x86/kernel/cpu/perf_event.h
> +++ b/arch/x86/kernel/cpu/perf_event.h
> @@ -660,6 +660,14 @@ static struct perf_pmu_events_attr event_attr_##v = {                      \
>         .event_str      = str,                                          \
>  };
>
> +#define EVENT_ATTR_STR_HT(_name, v, noht, ht)                          \
> +static struct perf_pmu_events_ht_attr event_attr_##v = {               \
> +       .attr           = __ATTR(_name, 0444, events_ht_sysfs_show, NULL),\
> +       .id             = 0,                                            \
> +       .event_str_noht = noht,                                         \
> +       .event_str_ht   = ht,                                           \
> +}
> +
>  extern struct x86_pmu x86_pmu __read_mostly;
>
>  static inline bool x86_pmu_has_lbr_callstack(void)
> @@ -919,6 +927,8 @@ int knc_pmu_init(void);
>
>  ssize_t events_sysfs_show(struct device *dev, struct device_attribute *attr,
>                           char *page);
> +ssize_t events_ht_sysfs_show(struct device *dev, struct device_attribute *attr,
> +                         char *page);
>
>  static inline int is_ht_workaround_enabled(void)
>  {
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f9828a4..ea2d830 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1166,6 +1166,13 @@ struct perf_pmu_events_attr {
>         const char *event_str;
>  };
>
> +struct perf_pmu_events_ht_attr {
> +       struct device_attribute attr;
> +       u64 id;
> +       const char *event_str_ht;
> +       const char *event_str_noht;
> +};
> +
>  ssize_t perf_event_sysfs_show(struct device *dev, struct device_attribute *attr,
>                               char *page);
>
> --
> 2.4.3
>
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