Messages in this thread | | | Date | Wed, 13 Mar 2024 12:02:50 +0000 | Subject | Re: [PATCH 05/10] drivers/perf: Use PERF_PMU_CAP_NO_SAMPLING consistently | From | Robin Murphy <> |
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On 2024-03-13 11:11 am, James Clark wrote: > > > On 12/03/2024 17:34, Robin Murphy wrote: >> Our system PMUs fundamentally cannot support the current notion of >> sampling events, so now that the core capability has been clarified, >> apply it consistently and purge yet more boilerplate. >> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com> >> --- >> drivers/perf/alibaba_uncore_drw_pmu.c | 6 +----- >> drivers/perf/amlogic/meson_ddr_pmu_core.c | 3 ++- >> drivers/perf/arm-cci.c | 3 ++- >> drivers/perf/arm-ccn.c | 12 +----------- >> drivers/perf/arm-cmn.c | 3 ++- >> drivers/perf/arm_cspmu/arm_cspmu.c | 17 ++++------------- >> drivers/perf/arm_dmc620_pmu.c | 4 ++-- >> drivers/perf/arm_dsu_pmu.c | 12 +----------- >> drivers/perf/arm_smmuv3_pmu.c | 6 +----- >> drivers/perf/cxl_pmu.c | 3 ++- >> drivers/perf/dwc_pcie_pmu.c | 5 +---- >> drivers/perf/fsl_imx8_ddr_perf.c | 3 ++- >> drivers/perf/fsl_imx9_ddr_perf.c | 3 ++- >> drivers/perf/hisilicon/hisi_pcie_pmu.c | 4 ++-- >> drivers/perf/hisilicon/hisi_uncore_pmu.c | 3 ++- >> drivers/perf/hisilicon/hns3_pmu.c | 4 ++-- >> drivers/perf/marvell_cn10k_ddr_pmu.c | 6 +----- >> drivers/perf/qcom_l2_pmu.c | 7 +------ >> drivers/perf/qcom_l3_pmu.c | 7 +------ >> drivers/perf/thunderx2_pmu.c | 4 ++-- >> drivers/perf/xgene_pmu.c | 4 ++-- >> 21 files changed, 36 insertions(+), 83 deletions(-) >> > [...] >> >> diff --git a/drivers/perf/arm-ccn.c b/drivers/perf/arm-ccn.c >> index ce26bb773a56..4114349e62dd 100644 >> --- a/drivers/perf/arm-ccn.c >> +++ b/drivers/perf/arm-ccn.c >> @@ -713,7 +713,6 @@ static void arm_ccn_pmu_event_release(struct perf_event *event) >> static int arm_ccn_pmu_event_init(struct perf_event *event) >> { >> struct arm_ccn *ccn; >> - struct hw_perf_event *hw = &event->hw; >> u32 node_xp, type, event_id; >> int valid; >> int i; >> @@ -721,16 +720,6 @@ static int arm_ccn_pmu_event_init(struct perf_event *event) >> >> ccn = pmu_to_arm_ccn(event->pmu); >> >> - if (hw->sample_period) { >> - dev_dbg(ccn->dev, "Sampling not supported!\n"); >> - return -EOPNOTSUPP; >> - } >> - >> - if (has_branch_stack(event)) { >> - dev_dbg(ccn->dev, "Can't exclude execution levels!\n"); >> - return -EINVAL; >> - } >> - > > [...] > >> diff --git a/drivers/perf/arm_dsu_pmu.c b/drivers/perf/arm_dsu_pmu.c >> index f5ea5acaf2f3..3424d165795c 100644 >> --- a/drivers/perf/arm_dsu_pmu.c >> +++ b/drivers/perf/arm_dsu_pmu.c >> @@ -544,23 +544,12 @@ static int dsu_pmu_event_init(struct perf_event *event) >> { >> struct dsu_pmu *dsu_pmu = to_dsu_pmu(event->pmu); >> >> - /* We don't support sampling */ >> - if (is_sampling_event(event)) { >> - dev_dbg(dsu_pmu->pmu.dev, "Can't support sampling events\n"); >> - return -EOPNOTSUPP; >> - } >> - >> /* We cannot support task bound events */ >> if (event->cpu < 0 || event->attach_state & PERF_ATTACH_TASK) { >> dev_dbg(dsu_pmu->pmu.dev, "Can't support per-task counters\n"); >> return -EINVAL; >> } >> >> - if (has_branch_stack(event)) { >> - dev_dbg(dsu_pmu->pmu.dev, "Can't support filtering\n"); >> - return -EINVAL; >> - } >> - > > I'm assuming that this and the other has_branch_stack() check were > removed because branch stacks don't actually do anything unless sampling > is enabled? > > It's a small difference that there is now no error message if you ask > for branch stacks, but it wouldn't have done anything anyway? I suppose > this error message was also not applied very consistently across the > different devices.
Right - the rarity of these checks, plus the fact that in both cases here they give a nonsensical debug message that has nothing whatsoever to do with the actual failing condition, seems to make it clear that they aren't realistically useful.
In general I don't see any good reason for a non-sampling event to be picky about the exact type of samples it isn't collecting.
Thanks, Robin.
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