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charset="us-ascii" Content-ID: <00601C4CE3AC2148B600DA5463E99FCF@namprd15.prod.outlook.com> MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SA1PR15MB5109.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3333bba2-b615-488e-63ee-08d96bd02162 X-MS-Exchange-CrossTenant-originalarrivaltime: 30 Aug 2021 16:06:30.5877 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 09wvzYGtTIM30VLXerpJ/Xbja0lvT5NQo+C5uH+JyiZPRK6ajCVAzq96yMS2xvRf24Ge8NTI/I77BjC5XTvSjQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR15MB5094 X-OriginatorOrg: fb.com X-Proofpoint-ORIG-GUID: 3r-YGwFDIRvxqDmxfI4CA7WCn4V6mmyc X-Proofpoint-GUID: 3r-YGwFDIRvxqDmxfI4CA7WCn4V6mmyc X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-08-30_05:2021-08-30,2021-08-30 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 impostorscore=0 bulkscore=0 clxscore=1015 priorityscore=1501 adultscore=0 phishscore=0 lowpriorityscore=0 mlxlogscore=999 suspectscore=0 malwarescore=0 mlxscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108300111 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Aug 30, 2021, at 3:43 AM, Peter Zijlstra wrote: > > On Thu, Aug 26, 2021 at 03:13:04PM -0700, Song Liu wrote: > >> Some data on intel_pmu_lbr_disable_all() and perf_pmu_disable(). >> >> With this patch, when fexit program triggers, intel_pmu_lbr_disable_all is >> used to stop the LBR, and the LBR is stopped after 6 extra branch records >> (see the full trace below). If we replace intel_pmu_lbr_disable_all in >> intel_pmu_snapshot_branch_stack() with perf_pmu_disable, the LBR is stopped >> after 19 extra branch records. This is still acceptable for systems with 32 >> LBR entries. But for systems with fewer entries, all the entries before >> fexit are flushed. Therefore, I suggest we take the short cut and stop LBR >> asap. >> >> >> LBR snapshot captured when we use intel_pmu_lbr_disable_all(): >> >> ID: 0 from intel_pmu_lbr_disable_all.part.10+37 to intel_pmu_lbr_disable_all.part.10+72 >> ID: 1 from intel_pmu_lbr_disable_all.part.10+33 to intel_pmu_lbr_disable_all.part.10+37 >> ID: 2 from intel_pmu_snapshot_branch_stack+51 to intel_pmu_lbr_disable_all.part.10+0 >> ID: 3 from __bpf_prog_enter+53 to intel_pmu_snapshot_branch_stack+0 >> ID: 4 from __bpf_prog_enter+8 to __bpf_prog_enter+38 >> ID: 5 from __brk_limit+473903158 to __bpf_prog_enter+0 >> ID: 6 from bpf_fexit_loop_test1+22 to __brk_limit+473903139 >> ID: 7 from bpf_fexit_loop_test1+20 to bpf_fexit_loop_test1+13 >> ID: 8 from bpf_fexit_loop_test1+20 to bpf_fexit_loop_test1+13 >> ID: 9 from bpf_fexit_loop_test1+20 to bpf_fexit_loop_test1+13 >> >> >> LBR snapshot captured when we use perf_pmu_disable(): >> >> ID: 0 from intel_pmu_lbr_disable_all+58 to intel_pmu_lbr_disable_all+93 >> ID: 1 from intel_pmu_lbr_disable_all+54 to intel_pmu_lbr_disable_all+58 >> ID: 2 from intel_pmu_disable_all+15 to intel_pmu_lbr_disable_all+0 >> ID: 3 from intel_pmu_pebs_disable_all+30 to intel_pmu_disable_all+15 >> ID: 4 from intel_pmu_disable_all+10 to intel_pmu_pebs_disable_all+0 >> ID: 5 from __intel_pmu_disable_all+49 to intel_pmu_disable_all+10 >> ID: 6 from intel_pmu_disable_all+5 to __intel_pmu_disable_all+0 >> ID: 7 from x86_pmu_disable+61 to intel_pmu_disable_all+0 >> ID: 8 from x86_pmu_disable+38 to x86_pmu_disable+41 >> ID: 9 from __x86_indirect_thunk_rax+16 to x86_pmu_disable+0 >> ID: 10 from __x86_indirect_thunk_rax+0 to __x86_indirect_thunk_rax+12 >> ID: 11 from perf_pmu_disable.part.122+4 to __x86_indirect_thunk_rax+0 >> ID: 12 from perf_pmu_disable+23 to perf_pmu_disable.part.122+0 >> ID: 13 from intel_pmu_snapshot_branch_stack+45 to perf_pmu_disable+0 >> ID: 14 from x86_get_pmu+35 to intel_pmu_snapshot_branch_stack+39 >> ID: 15 from intel_pmu_snapshot_branch_stack+34 to x86_get_pmu+0 >> ID: 16 from __bpf_prog_enter+53 to intel_pmu_snapshot_branch_stack+0 >> ID: 17 from __bpf_prog_enter+8 to __bpf_prog_enter+38 >> ID: 18 from __brk_limit+478056502 to __bpf_prog_enter+0 >> ID: 19 from bpf_fexit_loop_test1+22 to __brk_limit+478056483 >> ID: 20 from bpf_fexit_loop_test1+20 to bpf_fexit_loop_test1+13 >> ID: 21 from bpf_fexit_loop_test1+20 to bpf_fexit_loop_test1+13 > > Well, if you're willing to do something like: > >> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c >> index ac6fd2dabf6a2..a29649e7241cc 100644 >> --- a/arch/x86/events/intel/core.c >> +++ b/arch/x86/events/intel/core.c >> @@ -6283,8 +6283,11 @@ __init int intel_pmu_init(void) >> x86_pmu.lbr_nr = 0; >> } >> >> - if (x86_pmu.lbr_nr) >> + if (x86_pmu.lbr_nr) { >> pr_cont("%d-deep LBR, ", x86_pmu.lbr_nr); > > if (x86_pmu.disable_all == intel_pmu_disable_all) > >> + static_call_update(perf_snapshot_branch_stack, >> + intel_pmu_snapshot_branch_stack); >> + } >> >> intel_pmu_check_extra_regs(x86_pmu.extra_regs); >> >> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c >> index 9e6d6eaeb4cb6..7d4fe1d6e79ff 100644 >> --- a/arch/x86/events/intel/lbr.c >> +++ b/arch/x86/events/intel/lbr.c >> @@ -1862,3 +1862,16 @@ EXPORT_SYMBOL_GPL(x86_perf_get_lbr); >> struct event_constraint vlbr_constraint = >> __EVENT_CONSTRAINT(INTEL_FIXED_VLBR_EVENT, (1ULL << INTEL_PMC_IDX_FIXED_VLBR), >> FIXED_EVENT_FLAGS, 1, 0, PERF_X86_EVENT_LBR_SELECT); >> + >> +int intel_pmu_snapshot_branch_stack(struct perf_branch_snapshot *br_snapshot) >> +{ >> + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); >> + >> + intel_pmu_lbr_disable_all(); >> + intel_pmu_lbr_read(); >> + memcpy(br_snapshot->entries, cpuc->lbr_entries, >> + sizeof(struct perf_branch_entry) * x86_pmu.lbr_nr); >> + br_snapshot->nr = x86_pmu.lbr_nr; >> + intel_pmu_lbr_enable_all(false); >> + return 0; >> +} > > Then the above can assume perfmon > v2 and we can either inline > __intel_pmu_disable_all() or simply do the > wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL). I think can do perfmon > v2 only. > > One thing that needs checking, intel_pmu_disable_all() also clears > MSR_IA32_PEBS_ENABLE, is that really needed if we just want to inhibit > PMIs ? That is, will the PEBS machinery still trigger PMI if GLOBAL_CTRL > == 0 ? Actually, can we do something like: static void intel_pmu_disable_all(void) { intel_pmu_lbr_disable_all(); /* moved to the beginning */ __intel_pmu_disable_all(); intel_pmu_pebs_disable_all(); } int intel_pmu_snapshot_branch_stack(struct perf_branch_snapshot *br_snapshot) { struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); intel_pmu_disable_all(); /* call full pmu_disable */ intel_pmu_lbr_read(); memcpy(br_snapshot->entries, cpuc->lbr_entries, sizeof(struct perf_branch_entry) * x86_pmu.lbr_nr); br_snapshot->nr = x86_pmu.lbr_nr; intel_pmu_enable_all(false); return 0; } In this way, we still call intel_pmu_disable_all(), but since LBR is disabled at the beginning of it, we would not flush too many LBR entries. Thanks, Song