Messages in this thread | | | Subject | Re: [PATCH V2 04/23] perf/x86/intel: Support adaptive PEBSv4 | From | "Liang, Kan" <> | Date | Thu, 21 Mar 2019 20:40:03 -0400 |
| |
On 3/21/2019 5:20 PM, Peter Zijlstra wrote: > On Thu, Mar 21, 2019 at 01:56:44PM -0700, kan.liang@linux.intel.com wrote: >> @@ -933,6 +1001,34 @@ pebs_update_state(bool needed_cb, struct cpu_hw_events *cpuc, struct pmu *pmu) >> update = true; >> } >> >> + /* >> + * The PEBS record doesn't shrink on the del. Because to get >> + * an accurate config needs to go through all the existing pebs events. >> + * It's not necessary. >> + * There is no harmful for a bigger PEBS record, except little >> + * performance impacts. >> + * Also, for most cases, the same pebs config is applied for all >> + * pebs events. >> + */ >> + if (x86_pmu.intel_cap.pebs_baseline && add) { >> + u64 pebs_data_cfg; >> + >> + /* Clear pebs_data_cfg and pebs_record_size for first PEBS. */ >> + if (cpuc->n_pebs == 1) { >> + cpuc->pebs_data_cfg = 0; >> + cpuc->pebs_record_size = sizeof(struct pebs_basic); >> + } > > Argh, no. This is daft. The previous site was fine, it was just the > pebs_record_size assignment I'm confused about. > > Note how by setting ->pebs_data_cfs to 0, you force the below branch to > true and call adaptive_pebs_record_size_update() ? So _why_ do you have > to set pebs_record_size()? >
I think we have to reset both cpuc->pebs_data_cfg and cpuc->pebs_record_size. Because pebs_update_adaptive_cfg() can return 0. If so, adaptive_pebs_record_size_update() will not be called. The cpuc->pebs_record_size still use the stale data, which may be wrong.
I think there is no difference to reset them in first add or last del. If so, I will keep the code here unchanged.
I will prepare V3 to address other comments.
Thanks, Kan
>> + >> + pebs_data_cfg = pebs_update_adaptive_cfg(event); >> + >> + /* Update pebs_record_size if new event requires more data. */ >> + if (pebs_data_cfg & ~cpuc->pebs_data_cfg) { >> + cpuc->pebs_data_cfg |= pebs_data_cfg; >> + adaptive_pebs_record_size_update(); >> + update = true; >> + } >> + } >> + >> if (update) >> pebs_update_threshold(cpuc); >> }
| |