Re: [PATCH] torture: use ktime_t consistently

Boqun Feng
2016-06-22T01:57:33Z

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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@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. */

/* time 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);

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));

?

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

Regards,
Boqun

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

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