Hi German, Will,
On Fri, Oct 15, 2021 at 01:33:39PM +0100, German Gomez wrote:
[...]
$ ./perf record -vvv -e arm_spe/period=148576/u -S1000 -m16,16 -- taskset --cpu-list 0 stress --cpu 1 &
When testing Arm SPE snapshot mode with the command (it's quite similiar with up command but not exactly same):
# ./perf --debug verbose=3 record -e arm_spe/period=148576/u -C 0 -S1000 -m16,16 \ -- taskset --cpu-list 0 stress --cpu 1 & # kill -USR2 [pid_num]
... then I wait for long time and didn't stop the perf program, then I observed the output file contains many redundant events PERF_RECORD_AUX. E.g. in the shared perf data file [1], you could use below commands to see tons of the events PERF_RECORD_AUX which I only send only one USR2 signal for taking snapshot:
# perf report -D -i perf.data --stdio | grep -E 'RECORD_AUX' | wc -l 2245787
# perf report -D -i perf.data --stdio | grep -E 'SPE' . ... ARM SPE data: size 0x3e8 bytes Binary file (standard input) matches
I looked into the Arm SPE driver and found it doesn't really support free run mode for AUX ring buffer when the driver runs in snapshot mode, the pair functions perf_aux_output_end() and perf_aux_output_begin() are invoked when every time handle the interrupt. The detailed flow is:
arm_spe_pmu_irq_handler() `> arm_spe_pmu_buf_get_fault_act() `> arm_spe_perf_aux_output_end() `> set SPE registers `> perf_aux_output_end() `> arm_spe_perf_aux_output_begin() `> perf_aux_output_begin() `> set SPE registers
Seems to me, a possible solution is to add an extra parameter 'int in_interrupt' for functions arm_spe_perf_aux_output_end() and arm_spe_perf_aux_output_begin(), if this parameter is passed as 1 in the interrupt handling, these two functions should skip invoking perf_aux_output_end() and perf_aux_output_begin() so can avoid the redundant perf event PERF_RECORD_AUX.
arm_spe_pmu_irq_handler() `> arm_spe_pmu_buf_get_fault_act() `> arm_spe_perf_aux_output_end(..., in_interrupt=1) `> set SPE registers `> arm_spe_perf_aux_output_begin(..., in_interrupt=1) `> set SPE registers
P.s. I think Intel-PT has supported free run mode for snapshot mode, so it should not generate interrupt in this mode. Thus Intel-PT can avoid this issue, please see the code [2].
Thanks, Leo
[1] https://people.linaro.org/~leo.yan/spe/snapshot_test/perf.data [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch...