The following commit has been merged into the perf/urgent branch of tip:
Commit-ID: 312be9fc2234c8acfb8148a9f4c358b70d358dee Gitweb: https://git.kernel.org/tip/312be9fc2234c8acfb8148a9f4c358b70d358dee Author: Kan Liang kan.liang@linux.intel.com AuthorDate: Mon, 01 Apr 2024 06:33:20 -07:00 Committer: Ingo Molnar mingo@kernel.org CommitterDate: Wed, 03 Apr 2024 10:19:20 +02:00
perf/x86/intel/ds: Don't clear ->pebs_data_cfg for the last PEBS event
The MSR_PEBS_DATA_CFG MSR register is used to configure which data groups should be generated into a PEBS record, and it's shared among all counters.
If there are different configurations among counters, perf combines all the configurations.
The first perf command as below requires a complete PEBS record (including memory info, GPRs, XMMs, and LBRs). The second perf command only requires a basic group. However, after the second perf command is running, the MSR_PEBS_DATA_CFG register is cleared. Only a basic group is generated in a PEBS record, which is wrong. The required information for the first perf command is missed.
$ perf record --intr-regs=AX,SP,XMM0 -a -C 8 -b -W -d -c 100000003 -o /dev/null -e cpu/event=0xd0,umask=0x81/upp & $ sleep 5 $ perf record --per-thread -c 1 -e cycles:pp --no-timestamp --no-tid taskset -c 8 ./noploop 1000
The first PEBS event is a system-wide PEBS event. The second PEBS event is a per-thread event. When the thread is scheduled out, the intel_pmu_pebs_del() function is invoked to update the PEBS state. Since the system-wide event is still available, the cpuc->n_pebs is 1. The cpuc->pebs_data_cfg is cleared. The data configuration for the system-wide PEBS event is lost.
The (cpuc->n_pebs == 1) check was introduced in commit:
b6a32f023fcc ("perf/x86: Fix PEBS threshold initialization")
At that time, it indeed didn't hurt whether the state was updated during the removal, because only the threshold is updated.
The calculation of the threshold takes the last PEBS event into account.
However, since commit:
b752ea0c28e3 ("perf/x86/intel/ds: Flush PEBS DS when changing PEBS_DATA_CFG")
we delay the threshold update, and clear the PEBS data config, which triggers the bug.
The PEBS data config update scope should not be shrunk during removal.
[ mingo: Improved the changelog & comments. ]
Fixes: b752ea0c28e3 ("perf/x86/intel/ds: Flush PEBS DS when changing PEBS_DATA_CFG") Reported-by: Stephane Eranian eranian@google.com Signed-off-by: Kan Liang kan.liang@linux.intel.com Signed-off-by: Ingo Molnar mingo@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240401133320.703971-1-kan.liang@linux.intel.com --- arch/x86/events/intel/ds.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index 2641ba6..e010bfe 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -1237,11 +1237,11 @@ pebs_update_state(bool needed_cb, struct cpu_hw_events *cpuc, struct pmu *pmu = event->pmu;
/* - * Make sure we get updated with the first PEBS - * event. It will trigger also during removal, but - * that does not hurt: + * Make sure we get updated with the first PEBS event. + * During removal, ->pebs_data_cfg is still valid for + * the last PEBS event. Don't clear it. */ - if (cpuc->n_pebs == 1) + if ((cpuc->n_pebs == 1) && add) cpuc->pebs_data_cfg = PEBS_UPDATE_DS_SW;
if (needed_cb != pebs_needs_sched_cb(cpuc)) {