Re: [PATCH] torture: use ktime_t consistently

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

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@arndb.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@linux.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@linux.vnet.ibm.com>
    Acked-by: Arnd Bergmann <arnd@arndb.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. */
 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);
 		ret = torture_create_kthread(torture_shutdown, NULL,
 					     shutdown_task);
 	}