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SubjectRe: [PATCH v2] cpuidle: haltpoll: Add trace points for guest_halt_poll_ns grow/shrink
On Mon, 23 May 2022 23:53:32 +0000
Eiichi Tsukata <eiichi.tsukata@nutanix.com> wrote:

> @@ -91,16 +95,17 @@ static void adjust_poll_limit(struct cpuidle_device *dev, u64 block_ns)
> val = guest_halt_poll_ns;
>
> dev->poll_limit_ns = val;
> + trace_guest_halt_poll_ns_grow(smp_processor_id(), val, old);

Why are you passing in smp_processor_id()?

> } else if (block_ns > guest_halt_poll_ns &&
> guest_halt_poll_allow_shrink) {
> unsigned int shrink = guest_halt_poll_shrink;
>
> - val = dev->poll_limit_ns;
> if (shrink == 0)
> val = 0;
> else
> val /= shrink;
> dev->poll_limit_ns = val;
> + trace_guest_halt_poll_ns_shrink(smp_processor_id(), val, old);
> }
> }
>
> diff --git a/include/trace/events/power.h b/include/trace/events/power.h
> index af5018aa9517..db065af9c3c0 100644
> --- a/include/trace/events/power.h
> +++ b/include/trace/events/power.h
> @@ -500,6 +500,39 @@ DEFINE_EVENT(dev_pm_qos_request, dev_pm_qos_remove_request,
>
> TP_ARGS(name, type, new_value)
> );
> +
> +TRACE_EVENT(guest_halt_poll_ns,
> +
> + TP_PROTO(bool grow, unsigned int cpu_id,
> + unsigned int new, unsigned int old),
> +
> + TP_ARGS(grow, cpu_id, new, old),
> +
> + TP_STRUCT__entry(
> + __field(bool, grow)
> + __field(unsigned int, cpu_id)
> + __field(unsigned int, new)
> + __field(unsigned int, old)
> + ),
> +
> + TP_fast_assign(
> + __entry->grow = grow;
> + __entry->cpu_id = cpu_id;

You are wasting space to save the cpu_id, as the trace event already knows
what CPU it occurred on.

# echo 1 > events/sched/enable
# cat trace
# TASK-PID CPU# ||||| TIMESTAMP FUNCTION
# | | | ||||| | |
systemd-1 [004] ..... 15.872715: ftrace_boot_snapshot: ** Boot snapshot taken **
systemd-1 [001] ..... 22.555418: initcall_start: func=fuse_len_args+0x0/0x30 [fuse]
systemd-1 [001] ..... 22.555425: initcall_finish: func=fuse_len_args+0x0/0x30 [fuse] ret=0
modprobe-643 [006] ..... 26.737355: initcall_start: func=wmidev_evaluate_method+0x46/0x100 [wmi]
modprobe-643 [006] ..... 26.742491: initcall_finish: func=wmidev_evaluate_method+0x46/0x100 [wmi] ret=0
-- Steve



> + __entry->new = new;
> + __entry->old = old;
> + ),
> +
> + TP_printk("cpu %u: halt_poll_ns %u (%s %u)",
> + __entry->cpu_id,
> + __entry->new,
> + __entry->grow ? "grow" : "shrink",
> + __entry->old)
> +);
> +

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