From: Peter Zijlstra <peterz@infradead.org>
To: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
acme@kernel.org, mingo@redhat.com, kjain@linux.ibm.com,
kernel-team@fb.com
Subject: Re: [PATCH v3 bpf-next 1/3] perf: enable branch record for software events
Date: Tue, 31 Aug 2021 17:24:26 +0200 [thread overview]
Message-ID: <YS5Jqr60qHZ14+2g@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210830214106.4142056-2-songliubraving@fb.com>
On Mon, Aug 30, 2021 at 02:41:04PM -0700, Song Liu wrote:
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index ac6fd2dabf6a2..d28d0e12c112c 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2155,9 +2155,9 @@ static void __intel_pmu_disable_all(void)
>
> static void intel_pmu_disable_all(void)
> {
> + intel_pmu_lbr_disable_all();
> __intel_pmu_disable_all();
> intel_pmu_pebs_disable_all();
> - intel_pmu_lbr_disable_all();
> }
Hurmph... I'm not sure about that, I'd rather you sprinkle a few
__always_inline to ensure no actual function is called while you disable
things in the correct order.
You now still have a hole vs PMI.
> +static int
> +intel_pmu_snapshot_branch_stack(struct perf_branch_snapshot *br_snapshot)
> +{
> + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
Note that this requires preemption is disabled, then look at the
call-sites in your next patch and spot the problem...
> +
> + intel_pmu_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_enable_all(0);
> + return 0;
> +}
> +
> /*
> * Workaround for:
> * Intel Errata AAK100 (model 26)
> @@ -6283,9 +6297,15 @@ __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);
>
> + /* only support branch_stack snapshot for perfmon >= v2 */
> + 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);
>
> /* Support full width counters using alternative MSR range */
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 011cc5069b7ba..22807864e913b 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -13437,3 +13437,6 @@ struct cgroup_subsys perf_event_cgrp_subsys = {
> .threaded = true,
> };
> #endif /* CONFIG_CGROUP_PERF */
> +
> +DEFINE_STATIC_CALL_RET0(perf_snapshot_branch_stack,
> + perf_snapshot_branch_stack_t);
I'll squint and accept 82 characters :-)
next prev parent reply other threads:[~2021-08-31 15:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-30 21:41 [PATCH v3 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Song Liu
2021-08-30 21:41 ` [PATCH v3 bpf-next 1/3] perf: enable branch record for software events Song Liu
2021-08-30 22:05 ` Andrii Nakryiko
2021-08-31 15:24 ` Peter Zijlstra [this message]
2021-08-31 16:12 ` Song Liu
2021-08-30 21:41 ` [PATCH v3 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot Song Liu
2021-08-30 22:14 ` Andrii Nakryiko
2021-08-31 11:16 ` kernel test robot
2021-08-31 15:32 ` Peter Zijlstra
2021-08-31 16:41 ` Song Liu
2021-08-31 21:24 ` Song Liu
2021-08-31 21:37 ` Alexei Starovoitov
2021-08-30 21:41 ` [PATCH v3 bpf-next 3/3] selftests/bpf: add test for bpf_get_branch_snapshot Song Liu
2021-08-30 22:28 ` Andrii Nakryiko
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