Re: [PATCH v2] cpuidle: haltpoll: Add trace points for guest_halt_poll_ns grow/shrink

From: Steven Rostedt <rostedt@goodmis.org>
To: Eiichi Tsukata <eiichi.tsukata@nutanix.com>
Cc: rafael@kernel.org, daniel.lezcano@linaro.org, mingo@redhat.com,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
	joao.m.martins@oracle.com, mtosatti@redhat.com
Subject: Re: [PATCH v2] cpuidle: haltpoll: Add trace points for guest_halt_poll_ns grow/shrink
Date: Wed, 25 May 2022 12:02:48 -0400	[thread overview]
Message-ID: <20220525120248.5cb37817@gandalf.local.home> (raw)
In-Reply-To: <20220523235332.162966-1-eiichi.tsukata@nutanix.com>

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)
> +);
> +