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From: Andi Kleen <>
Subject: Add top down metrics to perf stat
Date: Fri, 15 Jan 2016 17:12:42 -0800
Message-ID: <> (raw)

[v2: Address review feedback.
Metrics are now always printed, but colored when crossing threshold.
--topdown implies --metric-only.
Various smaller fixes, see individual patches]

Note to reviewers: includes both tools and kernel patches.
The kernel patches are at the end.

This patchkit adds support for TopDown measurements to perf stat
It applies on top of my earlier metrics patchkit, posted

TopDown is intended to replace the frontend cycles idle/
backend cycles idle metrics in standard perf stat output.
These metrics are not reliable in many workloads, 
due to out of order effects.

This implements a new --topdown mode in perf stat
(similar to --transaction) that measures the pipe line
bottlenecks using standardized formulas. The measurement
can be all done with 5 counters (one fixed counter)

The result are four metrics:
FrontendBound, BackendBound, BadSpeculation, Retiring

that describe the CPU pipeline behavior on a high level.

FrontendBound and BackendBound
BadSpeculation is a higher

The full top down methology has many hierarchical metrics.
This implementation only supports level 1 which can be
collected without multiplexing. A full implementation
of top down on top of perf is available in pmu-tools toplev.

The current version works on Intel Core CPUs starting
with Sandy Bridge, and Atom CPUs starting with Silvermont.
In principle the generic metrics should be also implementable
on other out of order CPUs.

TopDown level 1 uses a set of abstracted metrics which
are generic to out of order CPU cores (although some
CPUs may not implement all of them):
topdown-total-slots   Available slots in the pipeline
topdown-slots-issued          Slots issued into the pipeline
topdown-slots-retired         Slots successfully retired
topdown-fetch-bubbles         Pipeline gaps in the frontend
topdown-recovery-bubbles  Pipeline gaps during recovery
                          from misspeculation
These metrics then allow to compute four useful metrics:
FrontendBound, BackendBound, Retiring, BadSpeculation.
The formulas to compute the metrics are generic, they
only change based on the availability on the abstracted
input values.
The kernel declares the events supported by the current
CPU and perf stat then computes the formulas based on the
available metrics.

Example output:

$ perf stat --topdown -I 100 ./BC1s
     0.100576098 frontend bound           retiring                 bad speculation          backend bound            
     0.100576098     8.83%                  48.93%                  35.24%                   7.00%               
     0.200800845     8.84%                  48.49%                  35.53%                   7.13%               
     0.300905983     8.73%                  48.64%                  35.58%                   7.05%            

On Hyper Threaded CPUs Top Down computes metrics per core instead of per logical CPU.
In this case perf stat automatically enables --per-core mode and also requires
global mode (-a) and avoiding other filters (no cgroup mode)

One side effect is that this may require root rights or a
kernel.perf_event_paranoid=-1 setting.  

On systems without Hyper Threading it can be used per process.

Full tree available in 
git:// perf/top-down-11

             reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-16  1:12 Andi Kleen [this message]
2016-01-16  1:12 ` [PATCH 01/11] perf, tools: Dont stop PMU parsing on alias parse error Andi Kleen
2016-01-16  1:12 ` [PATCH 02/11] perf, tools: Parse an .aggr-per-core event attribute Andi Kleen
2016-01-16  1:12 ` [PATCH 03/11] perf, tools, stat: Force --per-core mode for .aggr-per-core aliases Andi Kleen
2016-01-16  1:12 ` [PATCH 04/11] perf, tools, stat: Avoid fractional digits for integer scales Andi Kleen
2016-01-16  1:12 ` [PATCH 05/11] perf, tools, stat: Scale values by unit before metrics Andi Kleen
2016-01-16  1:12 ` [PATCH 06/11] perf, tools, stat: Basic support for TopDown in perf stat Andi Kleen
2016-01-16  1:12 ` [PATCH 07/11] perf, tools, stat: Add computation of TopDown formulas Andi Kleen
2016-01-16  1:12 ` [PATCH 08/11] perf, tools, stat: Add extra output of counter values with -v Andi Kleen
2016-01-16  1:12 ` [PATCH 09/11] x86, perf: Support sysfs files depending on SMT status Andi Kleen
2016-01-18 18:03   ` Peter Zijlstra
2016-01-18 18:06   ` Peter Zijlstra
2016-01-18 22:28     ` Andi Kleen
2016-01-16  1:12 ` [PATCH 10/11] x86, perf: Add Top Down events to Intel Core Andi Kleen
2016-01-16  1:12 ` [PATCH 11/11] x86, perf: Add Top Down events to Intel Atom Andi Kleen
  -- strict thread matches above, loose matches on Subject: below --
2016-05-20  0:09 Add top down metrics to perf stat Andi Kleen
2016-05-14  1:44 Andi Kleen
2016-05-16 12:58 ` Jiri Olsa
2016-05-19 23:51   ` Andi Kleen
2016-05-20  9:59     ` Jiri Olsa
2016-05-20 14:18       ` Andi Kleen
2016-05-20 10:24 ` Jiri Olsa
2016-05-05 23:03 Andi Kleen
2016-05-12  7:47 ` Jiri Olsa
2016-04-27 20:00 Andi Kleen
2016-04-04 20:41 Andi Kleen
2016-03-22 23:08 Andi Kleen
2016-03-27 11:27 ` Jiri Olsa
2016-03-27 15:22   ` Andi Kleen
2016-01-20  2:27 Andi Kleen
2015-08-08  1:06 Andi Kleen

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