Date:	Tue, 21 Jun 2016 20:27:24 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Boqun Feng <boqun.feng@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	Josh Triplett <josh@...htriplett.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] torture: use ktime_t consistently

On Wed, Jun 22, 2016 at 10:00:24AM +0800, Boqun Feng wrote:
> Hi Paul,
> 
> On Tue, Jun 21, 2016 at 11:39:46AM -0700, Paul E. McKenney wrote:
> > On Mon, Jun 20, 2016 at 09:29:56PM +0200, Arnd Bergmann wrote:
> > > On Monday, June 20, 2016 11:37:57 AM CEST Paul E. McKenney wrote:
> > > > On Mon, Jun 20, 2016 at 08:29:48PM +0200, Arnd Bergmann wrote:
> > > > > On Monday, June 20, 2016 11:21:05 AM CEST Paul E. McKenney wrote:
> > > > > > On Mon, Jun 20, 2016 at 05:56:40PM +0200, Arnd Bergmann wrote:
> > > > > >  
> > > > > > @@ -446,9 +447,9 @@ EXPORT_SYMBOL_GPL(torture_shuffle_cleanup);
> > > > > >   * Variables for auto-shutdown.  This allows "lights out" torture runs
> > > > > >   * to be fully scripted.
> > > > > >   */
> > > > > > -static int shutdown_secs;		/* desired test duration in seconds. */
> > > > > > +static ktime_t shutdown_ms;		/* desired test duration in seconds. */
> > > > > 
> > > > > the variable name is a bit odd.
> > > > 
> > > > The comment is certainly now wrong, good catch!
> > > > 
> > > > If there was an s_to_ktime(), I would have kept the old name, but I could
> > > > not find one.  Possibly due to me being blind...
> > > 
> > > I used "ktime_set(ssecs, 0)", which is almost what you want. Given that
> > > the majority of users of ktime_set() actually pass a zero nanoseconds portion,
> > > it would probably be nice to add secs_to_ktime() as well.
> > 
> > And there are quite a few that pass in zero for the seconds portion, and
> > many that pass in zero for both.
> > 
> > For the moment, I switched to ktime_set(), as you suggested.
> > 
> > > > > > @@ -511,10 +513,10 @@ int torture_shutdown_init(int ssecs, void (*cleanup)(void))
> > > > > >  {
> > > > > >  	int ret = 0;
> > > > > >  
> > > > > > -	shutdown_secs = ssecs;
> > > > > >  	torture_shutdown_hook = cleanup;
> > > > > > -	if (shutdown_secs > 0) {
> > > > > > -		shutdown_time = jiffies + shutdown_secs * HZ;
> > > > > > +	if (ssecs > 0) {
> > > > > > +		shutdown_ms = ms_to_ktime(ssecs * 1000ULL);
> > > > > > +		shutdown_time = ktime_add(ktime_get(), shutdown_ms);
> > > > > >  		ret = torture_create_kthread(torture_shutdown, NULL,
> > > > > >  					     shutdown_task);
> > > > > 
> > > > > and I picked ktime_set(ssecs, 0) instead of ms_to_ktime(ssecs * 1000ULL), but
> > > > > both differences are just cosmetic and should end up in exactly the
> > > > > same object code that I suggested. Unless we both made the same mistake,
> > > > > your version should be good too.
> > > > 
> > > > Thank you for looking it over!  My I apply your Acked-by:, Reviewed-by:,
> > > > or some such?
> > > 
> > > I had not looked over the original changes before, but have done that now,
> > > please add my 
> > > 
> > > Acked-by: Arnd Bergmann <arnd@...db.de>
> > 
> > Thank you!
> > 
> > > I found one small detail that you could change: instead of using
> > > HRTIMER_MODE_REL, you could actually use HRTIME_MODE_ABS and just
> > > pass the end time instead of computing the difference every time.
> > > 
> > > You still need to take the difference for printing, but you could
> > > do that in place then:
> > > 
> > >            if (verbose)
> > >                  pr_alert("%s" TORTURE_FLAG
> > >                           "torture_shutdown task: %llu ms remaining\n",
> > >                           torture_type, ktime_ms_delta(shutdown_time, ktime_get()));
> > 
> > Good point!  I did this, but used ktime_snap instead of ktime_get().
> > I have to capture ktime_snap anyway for the loop termination condition.
> > Updated commit below.
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 0a387a5b8718feace7aadd847937fdc336567a36
> > Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Date:   Sat Jun 18 07:45:43 2016 -0700
> > 
> >     torture: Convert torture_shutdown() to hrtimer
> >     
> >     Upcoming changes to the timer wheel introduce significant inaccuracy
> >     and possibly also an ultimate limit on timeout duration.  This is
> >     a problem for the current implementation of torture_shutdown() because
> >     (1) shutdown times are user-specified, and can therefore be quite
> >     long, and (2) the torture scripting will kill a test instance that
> >     runs for more than a few minutes longer than scheduled.  This commit
> >     therefore converts the torture_shutdown() timed waits to an hrtimer.
> >     
> >     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> >     Acked-by: Arnd Bergmann <arnd@...db.de>
> > 
> > diff --git a/kernel/torture.c b/kernel/torture.c
> > index 75961b3decfe..08f45621394a 100644
> > --- a/kernel/torture.c
> > +++ b/kernel/torture.c
> > @@ -43,6 +43,7 @@
> >  #include <linux/stat.h>
> >  #include <linux/slab.h>
> >  #include <linux/trace_clock.h>
> > +#include <linux/ktime.h>
> >  #include <asm/byteorder.h>
> >  #include <linux/torture.h>
> >  
> > @@ -446,9 +447,9 @@ EXPORT_SYMBOL_GPL(torture_shuffle_cleanup);
> >   * Variables for auto-shutdown.  This allows "lights out" torture runs
> >   * to be fully scripted.
> >   */
> > -static int shutdown_secs;		/* desired test duration in seconds. */
> > +static ktime_t shutdown_secs;		/* desired test duration in seconds. */
> >  static struct task_struct *shutdown_task;
> > -static unsigned long shutdown_time;	/* jiffies to system shutdown. */
> > +static ktime_t shutdown_time;		/* jiffies to system shutdown. */
> 
> 						/* time to system shutdown */ ?

Good eyes, fixed!

> >  static void (*torture_shutdown_hook)(void);
> >  
> >  /*
> > @@ -471,20 +472,20 @@ EXPORT_SYMBOL_GPL(torture_shutdown_absorb);
> >   */
> >  static int torture_shutdown(void *arg)
> >  {
> > -	long delta;
> > -	unsigned long jiffies_snap;
> > +	ktime_t ktime_snap;
> >  
> >  	VERBOSE_TOROUT_STRING("torture_shutdown task started");
> > -	jiffies_snap = jiffies;
> > -	while (ULONG_CMP_LT(jiffies_snap, shutdown_time) &&
> > +	ktime_snap = ktime_get();
> > +	while (ktime_before(ktime_snap, shutdown_time) &&
> >  	       !torture_must_stop()) {
> > -		delta = shutdown_time - jiffies_snap;
> >  		if (verbose)
> >  			pr_alert("%s" TORTURE_FLAG
> > -				 "torture_shutdown task: %lu jiffies remaining\n",
> > -				 torture_type, delta);
> > -		schedule_timeout_interruptible(delta);
> > -		jiffies_snap = jiffies;
> > +				 "torture_shutdown task: %llu ms remaining\n",
> > +				 torture_type,
> > +				 ktime_ms_delta(shutdown_time, ktime_snap));
> > +		set_current_state(TASK_INTERRUPTIBLE);
> > +		schedule_hrtimeout(&shutdown_time, HRTIMER_MODE_ABS);
> > +		ktime_snap = ktime_get();
> >  	}
> >  	if (torture_must_stop()) {
> >  		torture_kthread_stopping("torture_shutdown");
> > @@ -511,10 +512,10 @@ int torture_shutdown_init(int ssecs, void (*cleanup)(void))
> >  {
> >  	int ret = 0;
> >  
> > -	shutdown_secs = ssecs;
> >  	torture_shutdown_hook = cleanup;
> > -	if (shutdown_secs > 0) {
> > -		shutdown_time = jiffies + shutdown_secs * HZ;
> > +	if (ssecs > 0) {
> > +		shutdown_secs = ktime_set(ssecs, 0);
> > +		shutdown_time = ktime_add(ktime_get(), shutdown_secs);
> 
> As the 'shutdown_secs' here is only for 'shutdown_time' calculation, is
> it better that we kill 'shutdown_secs' entirely and calculate
> 'shutdown_time' via:
> 
> 	shutdown_time = ktime_add(ktime_get(), ktime_set(ssecs, 0)); 
> 
> ?

Good point, adjusted and removed shutdown_secs.

> (I found it a little weird that we don't have ktime_add_sec(), because
> we already have ktime_add_{n,m,u}s())

There does seem to be an odd set of primitives!

							Thanx, Paul

> Regards,
> Boqun
> 
> >  		ret = torture_create_kthread(torture_shutdown, NULL,
> >  					     shutdown_task);
> >  	}
> > 

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