From: Peter Zijlstra <peterz@infradead.org>
To: kan.liang@linux.intel.com
Cc: acme@redhat.com, mingo@kernel.org, linux-kernel@vger.kernel.org,
jolsa@kernel.org, eranian@google.com,
alexander.shishkin@linux.intel.com, ak@linux.intel.com
Subject: Re: [PATCH V6 09/14] perf/x86/intel: Support TopDown metrics on Ice Lake
Date: Tue, 21 Jul 2020 14:40:42 +0200 [thread overview]
Message-ID: <20200721124042.GX10769@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200717140554.22863-10-kan.liang@linux.intel.com>
On Fri, Jul 17, 2020 at 07:05:49AM -0700, kan.liang@linux.intel.com wrote:
> +static inline u64 icl_get_metrics_event_value(u64 metric, u64 slots, int idx)
> +{
> + u32 val;
> +
> + /*
> + * The metric is reported as an 8bit integer fraction
> + * suming up to 0xff.
> + * slots-in-metric = (Metric / 0xff) * slots
> + */
> + val = (metric >> ((idx - INTEL_PMC_IDX_METRIC_BASE) * 8)) & 0xff;
> + return mul_u64_u32_div(slots, val, 0xff);
> +}
> +
> +static void __icl_update_topdown_event(struct perf_event *event,
> + u64 slots, u64 metrics)
> +{
> + int idx = event->hw.idx;
> + u64 delta;
> +
> + if (is_metric_idx(idx))
> + delta = icl_get_metrics_event_value(metrics, slots, idx);
> + else
> + delta = slots;
> +
> + local64_add(delta, &event->count);
> +}
> +
> +/*
> + * Update all active Topdown events.
> + *
> + * The PERF_METRICS and Fixed counter 3 are read separately. The values may be
> + * modify by a NMI. PMU has to be disabled before calling this function.
> + */
> +static u64 icl_update_topdown_event(struct perf_event *event)
> +{
> + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> + struct perf_event *other;
> + u64 slots, metrics;
> + int idx;
> +
> + /* read Fixed counter 3 */
> + rdpmcl((3 | INTEL_PMC_FIXED_RDPMC_BASE), slots);
> + if (!slots)
> + return 0;
> +
> + /* read PERF_METRICS */
> + rdpmcl(INTEL_PMC_FIXED_RDPMC_METRICS, metrics);
> +
> + for_each_set_bit(idx, cpuc->active_mask, INTEL_PMC_IDX_TD_BE_BOUND + 1) {
> + if (!is_topdown_idx(idx))
> + continue;
> + other = cpuc->events[idx];
> + __icl_update_topdown_event(other, slots, metrics);
> + }
> +
> + /*
> + * Check and update this event, which may have been cleared
> + * in active_mask e.g. x86_pmu_stop()
> + */
> + if (event && !test_bit(event->hw.idx, cpuc->active_mask))
> + __icl_update_topdown_event(event, slots, metrics);
> +
> + /*
> + * Software is recommended to periodically clear both registers
> + * in order to maintain accurate measurements, which is required for
> + * certain scenarios that involve sampling metrics at high rates.
I'll maintain that that statement is clear as mud and therefore useless.
> + * Software should always write fixed counter 3 before write to
> + * PERF_METRICS.
> + */
> + wrmsrl(MSR_CORE_PERF_FIXED_CTR3, 0);
> + wrmsrl(MSR_PERF_METRICS, 0);
> +
> + return slots;
> +}
So in the normal case, this ends up calling into this function _5_
times, once for each event. Now the first time, it will actually do
something useful, but the other 4 times it's just wasting cycles.
Also, that for_each_set_bit() loop, trying to find the events to
update...
Can't we, instead, make the SLOTS update advance 5 running counters in
cpuc and feed the events off of that?
next prev parent reply other threads:[~2020-07-21 12:40 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 14:05 [PATCH V6 00/14] TopDown metrics support for Icelake kan.liang
2020-07-17 14:05 ` [PATCH V6 01/14] perf/x86: Use event_base_rdpmc for the RDPMC userspace support kan.liang
2020-07-17 14:05 ` [PATCH V6 02/14] perf/x86/intel: Name the global status bit in NMI handler kan.liang
2020-07-17 14:05 ` [PATCH V6 03/14] perf/x86/intel: Introduce the fourth fixed counter kan.liang
2020-07-20 16:20 ` Peter Zijlstra
2020-07-20 18:22 ` Liang, Kan
2020-07-17 14:05 ` [PATCH V6 04/14] perf/x86/intel: Move BTS index to 47 kan.liang
2020-07-17 14:05 ` [PATCH V6 05/14] perf/x86/intel: Fix the name of perf METRICS kan.liang
2020-07-17 14:05 ` [PATCH V6 06/14] perf/x86/intel: Use switch in intel_pmu_disable/enable_event kan.liang
2020-07-20 16:22 ` Peter Zijlstra
2020-07-20 19:02 ` Liang, Kan
2020-07-17 14:05 ` [PATCH V6 07/14] perf/x86/intel: Generic support for hardware TopDown metrics kan.liang
2020-07-20 17:41 ` Peter Zijlstra
2020-07-20 18:11 ` Liang, Kan
2020-07-21 9:43 ` Peter Zijlstra
2020-07-21 14:05 ` Liang, Kan
2020-07-21 14:25 ` peterz
2020-07-17 14:05 ` [PATCH V6 08/14] perf/x86: Add a macro for RDPMC offset of fixed counters kan.liang
2020-07-17 14:05 ` [PATCH V6 09/14] perf/x86/intel: Support TopDown metrics on Ice Lake kan.liang
2020-07-21 12:40 ` Peter Zijlstra [this message]
2020-07-21 14:23 ` Liang, Kan
2020-07-21 14:31 ` peterz
2020-07-21 15:50 ` Liang, Kan
2020-07-21 17:38 ` Andi Kleen
2020-07-21 19:20 ` Peter Zijlstra
2020-07-17 14:05 ` [PATCH V6 10/14] perf/x86/intel: Support per-thread RDPMC TopDown metrics kan.liang
2020-07-17 14:05 ` [PATCH V6 11/14] perf/x86/intel: Disable sample-read the slots and metrics events kan.liang
2020-07-21 13:10 ` Peter Zijlstra
2020-07-21 16:07 ` Liang, Kan
2020-07-21 19:18 ` Peter Zijlstra
2020-07-22 19:26 ` Liang, Kan
2020-07-17 14:05 ` [PATCH V6 12/14] perf, tools, stat: Support new per thread TopDown metrics kan.liang
2020-07-17 14:05 ` [PATCH V6 13/14] perf, tools, stat: Check Topdown Metric group kan.liang
2020-07-17 14:05 ` [PATCH V6 14/14] perf, tools: Add documentation for topdown metrics kan.liang
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