Re: [PATCH 12/21] perf/x86/intel/lbr: Support Architectural LBR

Peter Zijlstra
2020-06-19T19:08:49Z

On Fri, Jun 19, 2020 at 07:04:00AM -0700, kan.liang@linux.intel.com wrote:

> +static void intel_pmu_arch_lbr_enable(bool pmi)
> +{
> + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> + u64 debugctl, lbr_ctl = 0, orig_debugctl;
> +
> + if (pmi)
> + return;
> +
> + if (cpuc->lbr_ctl)
> + lbr_ctl = cpuc->lbr_ctl->config & x86_pmu.lbr_ctl_mask;
> + /*
> + * LBR callstack does not work well with FREEZE_LBRS_ON_PMI.
> + * If FREEZE_LBRS_ON_PMI is set, PMI near call/return instructions
> + * may be missed, that can lead to confusing results.
> + */
> + rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
> + orig_debugctl = debugctl;
> + if (lbr_ctl & ARCH_LBR_CALL_STACK)
> + debugctl &= ~DEBUGCTLMSR_FREEZE_LBRS_ON_PMI;
> + else
> + debugctl |= DEBUGCTLMSR_FREEZE_LBRS_ON_PMI;
> + if (orig_debugctl != debugctl)
> + wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
> +
> + wrmsrl(MSR_ARCH_LBR_CTL, lbr_ctl | ARCH_LBR_CTL_LBREN);
> +}

This is nearly a duplicate of the old one, surely we can do better?

> +static void intel_pmu_arch_lbr_restore(void *ctx)
> +{
> + struct x86_perf_task_context_arch_lbr *task_ctx = ctx;
> + struct x86_perf_arch_lbr_entry *entries = task_ctx->entries;
> + int i;
> +
> + /* Fast reset the LBRs before restore if the call stack is not full. */
> + if (!entries[x86_pmu.lbr_nr - 1].lbr_from)
> + intel_pmu_arch_lbr_reset();
> +
> + for (i = 0; i < x86_pmu.lbr_nr; i++) {
> + if (!entries[i].lbr_from)
> + break;
> + wrlbr_from(i, entries[i].lbr_from);
> + wrlbr_to(i, entries[i].lbr_to);
> + wrmsrl(MSR_ARCH_LBR_INFO_0 + i, entries[i].lbr_info);
> + }
> +}

This too looks very much like the old one.

> +static void intel_pmu_arch_lbr_save(void *ctx)
> +{
> + struct x86_perf_task_context_arch_lbr *task_ctx = ctx;
> + struct x86_perf_arch_lbr_entry *entries = task_ctx->entries;
> + int i;
> +
> + for (i = 0; i < x86_pmu.lbr_nr; i++) {
> + entries[i].lbr_from = rdlbr_from(i);
> + /* Only save valid branches. */
> + if (!entries[i].lbr_from)
> + break;
> + entries[i].lbr_to = rdlbr_to(i);
> + rdmsrl(MSR_ARCH_LBR_INFO_0 + i, entries[i].lbr_info);
> + }
> +
> + /* LBR call stack is not full. Reset is required in restore. */
> + if (i < x86_pmu.lbr_nr)
> + entries[x86_pmu.lbr_nr - 1].lbr_from = 0;
> +}

And again..

> +static void __intel_pmu_arch_lbr_read(struct cpu_hw_events *cpuc, int index,
> + u64 from, u64 to, u64 info)
> +{
> + u64 mis = 0, pred = 0, in_tx = 0, abort = 0, type = 0;
> + u32 br_type, to_plm;
> + u16 cycles = 0;
> +
> + if (x86_pmu.arch_lbr_mispred) {
> + mis = !!(info & ARCH_LBR_INFO_MISPRED);
> + pred = !mis;
> + }
> + in_tx = !!(info & ARCH_LBR_INFO_IN_TSX);
> + abort = !!(info & ARCH_LBR_INFO_TSX_ABORT);
> + if (x86_pmu.arch_lbr_timed_lbr &&
> + (info & ARCH_LBR_INFO_CYC_CNT_VALID))
> + cycles = (info & ARCH_LBR_INFO_CYC_CNT);
> +
> + /*
> + * Parse the branch type recorded in LBR_x_INFO MSR.
> + * Doesn't support OTHER_BRANCH decoding for now.
> + * OTHER_BRANCH branch type still rely on software decoding.
> + */
> + if (x86_pmu.arch_lbr_br_type) {
> + br_type = (info & ARCH_LBR_INFO_BR_TYPE) >> ARCH_LBR_INFO_BR_TYPE_OFFSET;
> +
> + if (br_type <= ARCH_LBR_BR_TYPE_KNOWN_MAX) {
> + to_plm = kernel_ip(to) ? X86_BR_KERNEL : X86_BR_USER;
> + type = arch_lbr_br_type_map[br_type] | to_plm;
> + }
> + }
> +
> + cpuc->lbr_entries[index].from = from;
> + cpuc->lbr_entries[index].to = to;
> + cpuc->lbr_entries[index].mispred = mis;
> + cpuc->lbr_entries[index].predicted = pred;
> + cpuc->lbr_entries[index].in_tx = in_tx;
> + cpuc->lbr_entries[index].abort = abort;
> + cpuc->lbr_entries[index].cycles = cycles;
> + cpuc->lbr_entries[index].type = type;
> + cpuc->lbr_entries[index].reserved = 0;
> +}
> +
> +static void intel_pmu_arch_lbr_read(struct cpu_hw_events *cpuc)
> +{
> + u64 from, to, info;
> + int i;
> +
> + for (i = 0; i < x86_pmu.lbr_nr; i++) {
> + from = rdlbr_from(i);
> + to = rdlbr_to(i);
> +
> + /*
> + * Read LBR entries until invalid entry (0s) is detected.
> + */
> + if (!from)
> + break;
> +
> + rdmsrl(MSR_ARCH_LBR_INFO_0 + i, info);
> +
> + __intel_pmu_arch_lbr_read(cpuc, i, from, to, info);
> + }
> +
> + cpuc->lbr_stack.nr = i;
> +}

> +static void intel_pmu_store_pebs_arch_lbrs(struct pebs_lbr *pebs_lbr,
> + struct cpu_hw_events *cpuc)
> +{
> + struct pebs_lbr_entry *lbr;
> + int i;
> +
> + for (i = 0; i < x86_pmu.lbr_nr; i++) {
> + lbr = &pebs_lbr->lbr[i];
> +
> + /*
> + * Read LBR entries until invalid entry (0s) is detected.
> + */
> + if (!lbr->from)
> + break;
> +
> + __intel_pmu_arch_lbr_read(cpuc, i, lbr->from,
> + lbr->to, lbr->info);
> + }
> +
> + cpuc->lbr_stack.nr = i;
> + intel_pmu_lbr_filter(cpuc);
> +}

Unless I'm reading cross-eyed again, that too is very similar to what we
already had.