linux-kernel - Re: [PATCH tip/core/rcu 2/5] rcu: Track CPU-hotplug duration statistics

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Date:	Thu, 30 Aug 2012 12:00:18 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 2/5] rcu: Track CPU-hotplug duration
 statistics

On Thu, Aug 30, 2012 at 11:45:09AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> 
> Many rcutorture runs include CPU-hotplug operations in their stress
> testing.  This commit accumulates statistics on the durations of these
> operations in deference to the recent concern about the overhead and
> latency of these operations.

How many jiffies, on average, do these operations take?  Measuring these
using jiffies seems highly prone to repeated rounding error.

> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  kernel/rcutorture.c |   42 +++++++++++++++++++++++++++++++++++++-----
>  1 files changed, 37 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
> index 86315d3..c6cf6ff 100644
> --- a/kernel/rcutorture.c
> +++ b/kernel/rcutorture.c
> @@ -176,8 +176,14 @@ static long n_rcu_torture_boosts;
>  static long n_rcu_torture_timers;
>  static long n_offline_attempts;
>  static long n_offline_successes;
> +static unsigned long sum_offline;
> +static int min_offline = -1;
> +static int max_offline;
>  static long n_online_attempts;
>  static long n_online_successes;
> +static unsigned long sum_online;
> +static int min_online = -1;
> +static int max_online;
>  static long n_barrier_attempts;
>  static long n_barrier_successes;
>  static struct list_head rcu_torture_removed;
> @@ -1214,11 +1220,13 @@ rcu_torture_printk(char *page)
>  		       n_rcu_torture_boost_failure,
>  		       n_rcu_torture_boosts,
>  		       n_rcu_torture_timers);
> -	cnt += sprintf(&page[cnt], "onoff: %ld/%ld:%ld/%ld ",
> -		       n_online_successes,
> -		       n_online_attempts,
> -		       n_offline_successes,
> -		       n_offline_attempts);
> +	cnt += sprintf(&page[cnt],
> +		       "onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
> +		       n_online_successes, n_online_attempts,
> +		       n_offline_successes, n_offline_attempts,
> +		       min_online, max_online,
> +		       min_offline, max_offline,
> +		       sum_online, sum_offline, HZ);
>  	cnt += sprintf(&page[cnt], "barrier: %ld/%ld:%ld",
>  		       n_barrier_successes,
>  		       n_barrier_attempts,
> @@ -1490,8 +1498,10 @@ static int __cpuinit
>  rcu_torture_onoff(void *arg)
>  {
>  	int cpu;
> +	unsigned long delta;
>  	int maxcpu = -1;
>  	DEFINE_RCU_RANDOM(rand);
> +	unsigned long starttime;
>  
>  	VERBOSE_PRINTK_STRING("rcu_torture_onoff task started");
>  	for_each_online_cpu(cpu)
> @@ -1509,6 +1519,7 @@ rcu_torture_onoff(void *arg)
>  				printk(KERN_ALERT "%s" TORTURE_FLAG
>  				       "rcu_torture_onoff task: offlining %d\n",
>  				       torture_type, cpu);
> +			starttime = jiffies;
>  			n_offline_attempts++;
>  			if (cpu_down(cpu) == 0) {
>  				if (verbose)
> @@ -1516,12 +1527,23 @@ rcu_torture_onoff(void *arg)
>  					       "rcu_torture_onoff task: offlined %d\n",
>  					       torture_type, cpu);
>  				n_offline_successes++;
> +				delta = jiffies - starttime;
> +				sum_offline += delta;
> +				if (min_offline < 0) {
> +					min_offline = delta;
> +					max_offline = delta;
> +				}
> +				if (min_offline > delta)
> +					min_offline = delta;
> +				if (max_offline < delta)
> +					max_offline = delta;
>  			}
>  		} else if (cpu_is_hotpluggable(cpu)) {
>  			if (verbose)
>  				printk(KERN_ALERT "%s" TORTURE_FLAG
>  				       "rcu_torture_onoff task: onlining %d\n",
>  				       torture_type, cpu);
> +			starttime = jiffies;
>  			n_online_attempts++;
>  			if (cpu_up(cpu) == 0) {
>  				if (verbose)
> @@ -1529,6 +1551,16 @@ rcu_torture_onoff(void *arg)
>  					       "rcu_torture_onoff task: onlined %d\n",
>  					       torture_type, cpu);
>  				n_online_successes++;
> +				delta = jiffies - starttime;
> +				sum_online += delta;
> +				if (min_online < 0) {
> +					min_online = delta;
> +					max_online = delta;
> +				}
> +				if (min_online > delta)
> +					min_online = delta;
> +				if (max_online < delta)
> +					max_online = delta;
>  			}
>  		}
>  		schedule_timeout_interruptible(onoff_interval * HZ);
> -- 
> 1.7.8
> 
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