Re: [PATCH] torture: use ktime_t consistently

Paul E. McKenney
2016-06-21T18:39:52Z

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);
}