Messages in this thread Patch in this message | | | Date | Wed, 24 May 2023 08:40:41 +0530 | Subject | Re: [PATCH V9 10/10] arm64/perf: Implement branch records save on PMU IRQ | From | Anshuman Khandual <> |
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On 5/23/23 20:09, James Clark wrote: > > > On 15/03/2023 05:14, Anshuman Khandual wrote: >> This modifies armv8pmu_branch_read() to concatenate live entries along with >> task context stored entries and then process the resultant buffer to create >> perf branch entry array for perf_sample_data. It follows the same principle >> like task sched out. >> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> --- > > [...] > >> void armv8pmu_branch_read(struct pmu_hw_events *cpuc, struct perf_event *event) >> { >> struct brbe_hw_attr *brbe_attr = (struct brbe_hw_attr *)cpuc->percpu_pmu->private; >> + struct arm64_perf_task_context *task_ctx = event->pmu_ctx->task_ctx_data; >> + struct brbe_regset live[BRBE_MAX_ENTRIES]; >> + int nr_live, nr_store; >> u64 brbfcr, brbcr; >> - int idx, loop1_idx1, loop1_idx2, loop2_idx1, loop2_idx2, count; >> >> brbcr = read_sysreg_s(SYS_BRBCR_EL1); >> brbfcr = read_sysreg_s(SYS_BRBFCR_EL1); >> @@ -739,36 +743,13 @@ void armv8pmu_branch_read(struct pmu_hw_events *cpuc, struct perf_event *event) >> write_sysreg_s(brbfcr | BRBFCR_EL1_PAUSED, SYS_BRBFCR_EL1); >> isb(); >> >> - /* Determine the indices for each loop */ >> - loop1_idx1 = BRBE_BANK0_IDX_MIN; >> - if (brbe_attr->brbe_nr <= BRBE_BANK_MAX_ENTRIES) { >> - loop1_idx2 = brbe_attr->brbe_nr - 1; >> - loop2_idx1 = BRBE_BANK1_IDX_MIN; >> - loop2_idx2 = BRBE_BANK0_IDX_MAX; >> - } else { >> - loop1_idx2 = BRBE_BANK0_IDX_MAX; >> - loop2_idx1 = BRBE_BANK1_IDX_MIN; >> - loop2_idx2 = brbe_attr->brbe_nr - 1; >> - } >> - >> - /* Loop through bank 0 */ >> - select_brbe_bank(BRBE_BANK_IDX_0); >> - for (idx = 0, count = loop1_idx1; count <= loop1_idx2; idx++, count++) { >> - if (!capture_branch_entry(cpuc, event, idx)) >> - goto skip_bank_1; >> - } >> - >> - /* Loop through bank 1 */ >> - select_brbe_bank(BRBE_BANK_IDX_1); >> - for (count = loop2_idx1; count <= loop2_idx2; idx++, count++) { >> - if (!capture_branch_entry(cpuc, event, idx)) >> - break; >> - } >> - >> -skip_bank_1: >> - cpuc->branches->branch_stack.nr = idx; >> - cpuc->branches->branch_stack.hw_idx = -1ULL; >> + nr_live = capture_brbe_regset(brbe_attr, live); >> + nr_store = task_ctx->nr_brbe_records; >> + nr_store = stitch_stored_live_entries(task_ctx->store, live, nr_store, >> + nr_live, brbe_attr->brbe_nr); >> + process_branch_entries(cpuc, event, task_ctx->store, nr_store); > > Hi Anshuman, > > With the following command I get a crash: > > perf record --branch-filter any,save_type -a -- ls > > [ 101.171822] Unable to handle kernel NULL pointer dereference at > virtual address 0000000000000600 > ... > [145380.414654] Call trace: > [145380.414739] armv8pmu_branch_read+0x7c/0x578 > [145380.414895] armv8pmu_handle_irq+0x104/0x1c0 > [145380.415043] armpmu_dispatch_irq+0x38/0x70 > [145380.415209] __handle_irq_event_percpu+0x124/0x3b8 > [145380.415392] handle_irq_event+0x54/0xc8 > [145380.415567] handle_fasteoi_irq+0x100/0x1e0 > [145380.415718] generic_handle_domain_irq+0x38/0x58 > [145380.415895] gic_handle_irq+0x5c/0x130 > [145380.416025] call_on_irq_stack+0x24/0x58 > [145380.416173] el1_interrupt+0x74/0xc0 > [145380.416321] el1h_64_irq_handler+0x18/0x28 > [145380.416475] el1h_64_irq+0x64/0x68 > [145380.416604] smp_call_function_single+0xe8/0x1f0 > [145380.416745] event_function_call+0xbc/0x1c8 > [145380.416919] _perf_event_enable+0x84/0xa0 > [145380.417069] perf_ioctl+0xe8/0xd68 > [145380.417204] __arm64_sys_ioctl+0x9c/0xe0 > [145380.417353] invoke_syscall+0x4c/0x120 > [145380.417523] el0_svc_common+0xd0/0x120 > [145380.417693] do_el0_svc+0x3c/0xb8 > [145380.417859] el0_svc+0x50/0xc0 > [145380.418004] el0t_64_sync_handler+0x84/0xf0 > [145380.418160] el0t_64_sync+0x190/0x198 > > When using --branch-filter any,u without -a it seems to be fine so could > be that task_ctx is null in per-cpu mode, or something to do with the > userspace only flag?
It's task_ctx is null in per-cpu mode, because armv8pmu_branch_read() used event->pmu_ctx->task_ctx_data in per-cpu mode where it would not have been allocated as well. Following change fixes the problem.
diff --git a/drivers/perf/arm_brbe.c b/drivers/perf/arm_brbe.c index 9e441141a2c3..c8fd581eacf9 100644 --- a/drivers/perf/arm_brbe.c +++ b/drivers/perf/arm_brbe.c @@ -744,12 +744,17 @@ void armv8pmu_branch_read(struct pmu_hw_events *cpuc, struct perf_event *event) isb(); nr_live = capture_brbe_regset(brbe_attr, live); - nr_store = task_ctx->nr_brbe_records; - nr_store = stitch_stored_live_entries(task_ctx->store, live, nr_store, - nr_live, brbe_attr->brbe_nr); - process_branch_entries(cpuc, event, task_ctx->store, nr_store); + if (event->ctx->task) { + nr_store = task_ctx->nr_brbe_records; + nr_store = stitch_stored_live_entries(task_ctx->store, live, nr_store, + nr_live, brbe_attr->brbe_nr); + process_branch_entries(cpuc, event, task_ctx->store, nr_store); + task_ctx->nr_brbe_records = 0; + } else { + process_branch_entries(cpuc, event, live, nr_live); + } + process_branch_aborts(cpuc); - task_ctx->nr_brbe_records = 0; /* Unpause the buffer */ write_sysreg_s(brbfcr & ~BRBFCR_EL1_PAUSED, SYS_BRBFCR_EL1);
> > I'm also wondering if it's possible to collapse some of the last 5 > commits? They seem to mostly modify things in brbe.c which is a new file > so the history probably isn't important at this point it just makes it a > bit harder to review.
[PATCH 6/10] enables base perf branch stack sampling on arm64 platform via BRBE and then subsequent patches represent logical progression up until save-stitch mechanism is implemented both during normal PMU IRQ and task switch callbacks.
> >> process_branch_aborts(cpuc); >> + task_ctx->nr_brbe_records = 0; >> >> /* Unpause the buffer */ >> write_sysreg_s(brbfcr & ~BRBFCR_EL1_PAUSED, SYS_BRBFCR_EL1);
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