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Commit ce071ea9 authored by Neil Leeder's avatar Neil Leeder Committed by Matt Wagantall
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Perf: arm64: tracectr: initialize counts after hotplug 



Due to the mismatch between counter values saved across CPU hotplug
by perf and tracecounter logic, incorrect values are calculated
for a cpu's first entry in trace buffer.

Ignore the first entry when CPU comes out of hotplug and set previous
counter values in this scenario.

Change-Id: I0a61943d14aa3bc96b50f7ed05e25c592be9aa35
Signed-off-by: default avatarNeil Leeder <nleeder@codeaurora.org>
parent 0a51bd75

arch/arm64/kernel/perf_debug.c

+1 −0
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ static char *descriptions = 
	" 6 Perf: arm64: Add debugfs node to clear PMU\n"

	" 7 Perf: arm64: Update PMU force reset\n"

	" 9 Perf: arm64: make request irq pmu-dependent\n"

	"10 Perf: arm64: tracectr: initialize counts after hotplug\n"

;



static ssize_t desc_read(struct file *fp, char __user *buf,

arch/arm64/kernel/perf_trace_counters.c

+55 −4
Original line number Diff line number Diff line
@@ -22,19 +22,68 @@ static unsigned int tp_pid_state; 
DEFINE_PER_CPU(u32, previous_ccnt);

DEFINE_PER_CPU(u32[NUM_L1_CTRS], previous_l1_cnts);

DEFINE_PER_CPU(u32, old_pid);

DEFINE_PER_CPU(u32, hotplug_flag);



static int tracectr_cpu_hotplug_notifier(struct notifier_block *self,

					 unsigned long action, void *hcpu)

{

	unsigned long cpu = (unsigned long)hcpu;



	if ((action & (~CPU_TASKS_FROZEN)) == CPU_STARTING)

		per_cpu(hotplug_flag, cpu) = 1;



	return NOTIFY_OK;

}



static struct notifier_block tracectr_cpu_hotplug_notifier_block = {

	.notifier_call = tracectr_cpu_hotplug_notifier,

};



static void setup_prev_cnts(u32 cpu)

{

	int i;

	u32 cnten_val;



	asm volatile("mrs %0, pmcntenset_el0" : "=r" (cnten_val));

	/* Disable all the counters that were enabled */

	asm volatile("msr pmcntenclr_el0, %0" : : "r" (cnten_val));

	if (cnten_val & CC)

		asm volatile("mrs %0, pmccntr_el0"

			: "=r"(per_cpu(previous_ccnt, cpu)));



	for (i = 0; i < NUM_L1_CTRS; i++) {

		if (cnten_val & (1 << i)) {

			/* Select */

			asm volatile("msr pmselr_el0, %0" : : "r"(i));

			isb();

			/* Read value */

			asm volatile("mrs %0, pmxevcntr_el0"

				: "=r"(per_cpu(previous_l1_cnts[i], cpu)));

		}

	}

	/* Enable all the counters that were disabled */

	asm volatile("msr pmcntenset_el0, %0" : : "r" (cnten_val));

}



void tracectr_notifier(void *ignore, struct task_struct *prev,

					struct task_struct *next)

{

	int current_pid;

	u32 cpu = next->on_cpu;

	u32 cpu = task_thread_info(next)->cpu;



	if (tp_pid_state != 1)

		return;

	current_pid = next->pid;

	if (per_cpu(old_pid, cpu) != -1)

	if (per_cpu(old_pid, cpu) != -1) {



		if (per_cpu(hotplug_flag, cpu) == 1) {

			per_cpu(hotplug_flag, cpu) = 0;

			setup_prev_cnts(cpu);

		} else {

			trace_sched_switch_with_ctrs(per_cpu(old_pid, cpu),

						     current_pid);

		}

	}

	per_cpu(old_pid, cpu) = current_pid;

}
@@ -115,11 +164,13 @@ int __init init_tracecounters(void) 
	}

	for_each_possible_cpu(cpu)

		per_cpu(old_pid, cpu) = -1;

	register_cpu_notifier(&tracectr_cpu_hotplug_notifier_block);

	return 0;

}



int __exit exit_tracecounters(void)

{

	unregister_cpu_notifier(&tracectr_cpu_hotplug_notifier_block);

	return 0;

}

late_initcall(init_tracecounters);