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Date:   Wed, 31 Aug 2022 11:40:22 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Ian Rogers <irogers@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Thomas Richter <tmricht@linux.ibm.com>,
        James Clark <james.clark@arm.com>,
        Miaoqian Lin <linmq006@gmail.com>,
        John Garry <john.garry@huawei.com>,
        Zhengjun Xing <zhengjun.xing@linux.intel.com>,
        Florian Fischer <florian.fischer@muhq.space>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        perry.taylor@intel.com, caleb.biggers@intel.com,
        kshipra.bopardikar@intel.com, Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH v1 5/8] perf topology: Add core_wide
Message-ID: <Yw9y1mEW7BhNvStT@kernel.org>
References: <20220830164846.401143-1-irogers@google.com>
 <20220830164846.401143-6-irogers@google.com>
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Em Tue, Aug 30, 2022 at 09:48:43AM -0700, Ian Rogers escreveu:
> It is possible to optimize metrics when all SMT threads (CPUs) on a
> core are measuring events in system wide mode. For example, TMA
> metrics defines CORE_CLKS for Sandybrdige as:
> 
> if SMT is disabled:
>   CPU_CLK_UNHALTED.THREAD
> if SMT is enabled and recording on all SMT threads:
>   CPU_CLK_UNHALTED.THREAD_ANY / 2
> if SMT is enabled and not recording on all SMT threads:
>   (CPU_CLK_UNHALTED.THREAD/2)*
>   (1+CPU_CLK_UNHALTED.ONE_THREAD_ACTIVE/CPU_CLK_UNHALTED.REF_XCLK )
> 
> That is two more events are necessary when not gathering counts on all
> SMT threads. To distinguish all SMT threads on a core vs system wide
> (all CPUs) call the new property core wide.  Add a core wide test that
> determines the property from user requested CPUs, the topology and
> system wide. System wide is required as other processes running on a
> SMT thread will change the counts.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/util/cputopo.c | 46 +++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/cputopo.h |  3 +++
>  tools/perf/util/smt.c     | 14 ++++++++++++
>  tools/perf/util/smt.h     |  7 ++++++
>  4 files changed, 70 insertions(+)
> 
> diff --git a/tools/perf/util/cputopo.c b/tools/perf/util/cputopo.c
> index 511002e52714..1a3ff6449158 100644
> --- a/tools/perf/util/cputopo.c
> +++ b/tools/perf/util/cputopo.c
> @@ -172,6 +172,52 @@ bool cpu_topology__smt_on(const struct cpu_topology *topology)
>  	return false;
>  }
>  
> +bool cpu_topology__core_wide(const struct cpu_topology *topology,
> +			     const char *user_requested_cpu_list)
> +{
> +	struct perf_cpu_map *user_requested_cpus;
> +
> +	/*
> +	 * If user_requested_cpu_list is empty then all CPUs are recorded and so
> +	 * core_wide is true.
> +	 */
> +	if (!user_requested_cpu_list)
> +		return true;
> +
> +	user_requested_cpus = perf_cpu_map__new(user_requested_cpu_list);

Don't we need a NULL test here?

> +	/* Check that every user requested CPU is the complete set of SMT threads on a core. */
> +	for (u32 i = 0; i < topology->core_cpus_lists; i++) {
> +		const char *core_cpu_list = topology->core_cpus_list[i];
> +		struct perf_cpu_map *core_cpus = perf_cpu_map__new(core_cpu_list);

Here too, no?

> +		struct perf_cpu cpu;
> +		int idx;
> +		bool has_first, first = true;
> +
> +		perf_cpu_map__for_each_cpu(cpu, idx, core_cpus) {
> +			if (first) {
> +				has_first = perf_cpu_map__has(user_requested_cpus, cpu);
> +				first = false;
> +			} else {
> +				/*
> +				 * If the first core CPU is user requested then
> +				 * all subsequent CPUs in the core must be user
> +				 * requested too. If the first CPU isn't user
> +				 * requested then none of the others must be
> +				 * too.
> +				 */
> +				if (perf_cpu_map__has(user_requested_cpus, cpu) != has_first) {
> +					perf_cpu_map__put(core_cpus);
> +					perf_cpu_map__put(user_requested_cpus);
> +					return false;
> +				}
> +			}
> +		}
> +		perf_cpu_map__put(core_cpus);
> +	}
> +	perf_cpu_map__put(user_requested_cpus);
> +	return true;
> +}
> +
>  static bool has_die_topology(void)
>  {
>  	char filename[MAXPATHLEN];
> diff --git a/tools/perf/util/cputopo.h b/tools/perf/util/cputopo.h
> index 469db775a13c..969e5920a00e 100644
> --- a/tools/perf/util/cputopo.h
> +++ b/tools/perf/util/cputopo.h
> @@ -60,6 +60,9 @@ struct cpu_topology *cpu_topology__new(void);
>  void cpu_topology__delete(struct cpu_topology *tp);
>  /* Determine from the core list whether SMT was enabled. */
>  bool cpu_topology__smt_on(const struct cpu_topology *topology);
> +/* Are the sets of SMT siblings all enabled or all disabled in user_requested_cpus. */
> +bool cpu_topology__core_wide(const struct cpu_topology *topology,
> +			     const char *user_requested_cpu_list);
>  
>  struct numa_topology *numa_topology__new(void);
>  void numa_topology__delete(struct numa_topology *tp);
> diff --git a/tools/perf/util/smt.c b/tools/perf/util/smt.c
> index ce90c4ee4138..994e9e418227 100644
> --- a/tools/perf/util/smt.c
> +++ b/tools/perf/util/smt.c
> @@ -21,3 +21,17 @@ bool smt_on(const struct cpu_topology *topology)
>  	cached = true;
>  	return cached_result;
>  }
> +
> +bool core_wide(bool system_wide, const char *user_requested_cpu_list,
> +	       const struct cpu_topology *topology)
> +{
> +	/* If not everything running on a core is being recorded then we can't use core_wide. */
> +	if (!system_wide)
> +		return false;
> +
> +	/* Cheap case that SMT is disabled and therefore we're inherently core_wide. */
> +	if (!smt_on(topology))
> +		return true;
> +
> +	return cpu_topology__core_wide(topology, user_requested_cpu_list);
> +}
> diff --git a/tools/perf/util/smt.h b/tools/perf/util/smt.h
> index e26999c6b8d4..ae9095f2c38c 100644
> --- a/tools/perf/util/smt.h
> +++ b/tools/perf/util/smt.h
> @@ -7,4 +7,11 @@ struct cpu_topology;
>  /* Returns true if SMT (aka hyperthreading) is enabled. */
>  bool smt_on(const struct cpu_topology *topology);
>  
> +/*
> + * Returns true when system wide and all SMT threads for a core are in the
> + * user_requested_cpus map.
> + */
> +bool core_wide(bool system_wide, const char *user_requested_cpu_list,
> +	       const struct cpu_topology *topology);
> +
>  #endif /* __SMT_H */
> -- 
> 2.37.2.672.g94769d06f0-goog

-- 

- Arnaldo