perf/Documentation/perf-arm-spe.txt

1 perf-arm-spe(1)
5 ----
6 perf-arm-spe - Support for Arm Statistical Profiling Extension within Perf tools
9 --------
11 'perf record' -e arm_spe//
14 -----------
17  events down to individual instructions. Rather than being interrupt-driven, it picks an
33 architectural instructions or all micro-ops. Sampling happens at a programmable interval. The
35 sample. This minimum interval is used by the driver if no interval is specified. A pseudo-random
62 ----------------
64 Up until this point no decoding of the SPE data was done by either the kernel or Perf. Only when the
66 the data, Perf generates "synthetic samples" as if these were generated at the time of the
67 recording. These samples are the same as if normal sampling was done by Perf without using SPE,
72 -------------
74  - Sampling, rather than tracing, cuts down the profiling problem to something more manageable for
77  - Allows precise attribution data, including: Full PC of instruction, data virtual and physical
80  - Allows correlation between an instruction and events, such as TLB and cache miss. (Data source
84 However, SPE does not provide any call-graph information, and relies on statistical methods.
87 ----------
93 The 'sample_collision' PMU event can be used to determine the number of lost samples. Although this
95 number for samples dropped that would have made it through the filter, but can be a rough
99 -----------------------------------------
101 If an implementation samples micro-operations instead of instructions, the results of sampling must
104 For example, if a given instruction A is always converted into two micro-operations, A0 and A1, it
111 -------------------
128 Capturing SPE with perf command-line tools
129 ------------------------------------------
131 You can record a session with SPE samples:
133   perf record -e arm_spe// -- ./mybench
135 The sample period is set from the -c option, and because the minimum interval is used by default
141 These are placed between the // in the event and comma separated. For example '-e
144   branch_filter=1     - collect branches only (PMSFCR.B)
145   event_filter=<mask> - filter on specific events (PMSEVFR) - see bitfield description below
146   jitter=1            - use jitter to avoid resonance when sampling (PMSIRR.RND)
147   load_filter=1       - collect loads only (PMSFCR.LD)
148   min_latency=<n>     - collect only samples with this latency or higher* (PMSLATFR)
149 …pa_enable=1         - collect physical address (as well as VA) of loads/stores (PMSCR.PA) - requir…
150 …pct_enable=1        - collect physical timestamp instead of virtual timestamp (PMSCR.PCT) - requir…
151   store_filter=1      - collect stores only (PMSFCR.ST)
152   ts_enable=1         - enable timestamping with value of generic timer (PMSCR.TS)
159   bit 1     - instruction retired (i.e. omit speculative instructions)
160   bit 3     - L1D refill
161   bit 5     - TLB refill
162   bit 7     - mispredict
163   bit 11    - misaligned access
167   perf record -e arm_spe/event_filter=2/ -- ./mybench
171   perf record -e arm_spe/event_filter=0x80/ -- ./mybench
176 By default perf report and perf script will assign samples to separate groups depending on the
178 them, the samples in these groups are not necessarily unique. For example perf report shows these
181   Available samples
184   21 l1d-miss
185   897 l1d-access
186   5 llc-miss
187   7 llc-access
188   2 tlb-miss
189   1K tlb-access
190   36 branch-miss
191   0 remote-access
196 To get a full list of unique samples that are not sorted into groups, set the itrace option to
197 generate 'instruction' samples. The period option is also taken into account, so set it to 1
200   perf report --itrace=i1i
202 Memory access details are also stored on the samples and this can be viewed with:
204   perf report --mem-mode
209  - "Cannot find PMU `arm_spe'. Missing kernel support?"
214  - "Arm SPE CONTEXT packets not found in the traces."
217    assigning PIDs to kernel samples. For userspace sampling this can be ignored.
219  - Excessively large perf.data file size
225 --------
227 linkperf:perf-record[1], linkperf:perf-script[1], linkperf:perf-report[1],
228 linkperf:perf-inject[1]