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Message-Id: <200909041642.03774.rjw@sisk.pl>
Date: Fri, 4 Sep 2009 16:42:03 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Alan Stern <stern@...land.harvard.edu>,
"linux-pm" <linux-pm@...ts.linux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
Pavel Machek <pavel@....cz>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
Arjan van de Ven <arjan@...radead.org>,
Zhang Rui <rui.zhang@...el.com>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 10] PM: Measure suspend and resume times for individual devices (was: Re: [PATCH 2/6] PM: Asynchronous resume of devices)
On Friday 04 September 2009, Ingo Molnar wrote:
>
> * Rafael J. Wysocki <rjw@...k.pl> wrote:
>
> > On Monday 31 August 2009, Ingo Molnar wrote:
> > >
> > > * Rafael J. Wysocki <rjw@...k.pl> wrote:
> > >
> > > > On Monday 31 August 2009, Ingo Molnar wrote:
> > > > >
> > > > > * Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > > >
> > > > > > On Sunday 30 August 2009, Rafael J. Wysocki wrote:
> > > > > > > On Sunday 30 August 2009, Alan Stern wrote:
> > > > > > > > On Sat, 29 Aug 2009, Rafael J. Wysocki wrote:
> > > > > > > >
> > > > > > > > > I only wanted to say that the advantage is not really that "big". :-)
> > > > > > > > >
> > > > > > > > > > I must agree, 14 threads isn't a lot. But at the moment that number is
> > > > > > > > > > random, not under your control.
> > > > > > > > >
> > > > > > > > > It's not directly controlled, but there are some interactions between the
> > > > > > > > > async threads, the main threads and the async framework that don't allow this
> > > > > > > > > number to grow too much.
> > > > > > > > >
> > > > > > > > > IMO it sometimes is better to allow things to work themselves out, as long as
> > > > > > > > > they don't explode, than to try to keep everything under strict control. YMMV.
> > > > > > > >
> > > > > > > > For testing purposes it would be nice to have a one-line summary for
> > > > > > > > each device containing a thread ID, start timestamp, end timestamp, and
> > > > > > > > elapsed time. With that information you could evaluate the amount of
> > > > > > > > parallelism and determine where the bottlenecks are. It would give a
> > > > > > > > much more detailed picture of the entire process than the total time of
> > > > > > > > your recent patch 9.
> > > > > > >
> > > > > > > Of course it would. I think I'll implement it.
> > > > > >
> > > > > > OK, below is a patch for that. It only prints the time elapsed, because the
> > > > > > timestamps themselves can be obtained from the usual kernel timestamping.
> > > > > >
> > > > > > It's on top of all the previous patches.
> > > > > >
> > > > > > Thanks,
> > > > > > Rafael
> > > > > >
> > > > > > ---
> > > > > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > > > > Subject: PM: Measure suspend and resume times for individual devices
> > > > > >
> > > > > > If verbose PM debugging is enabled, measure and print the time of
> > > > > > suspending and resuming of individual devices.
> > > > > >
> > > > > > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > > > > > ---
> > > > > > drivers/base/power/main.c | 51 +++++++++++++++++++++++++++++++++++++++++-----
> > > > > > kernel/power/swsusp.c | 2 -
> > > > > > 2 files changed, 47 insertions(+), 6 deletions(-)
> > > > > >
> > > > > > Index: linux-2.6/drivers/base/power/main.c
> > > > > > ===================================================================
> > > > > > --- linux-2.6.orig/drivers/base/power/main.c
> > > > > > +++ linux-2.6/drivers/base/power/main.c
> > > > > > @@ -442,11 +442,11 @@ static bool pm_op_started(struct device
> > > > > > */
> > > > > > int pm_time_elapsed(struct timeval *start, struct timeval *stop)
> > > > > > {
> > > > > > - s64 elapsed_centisecs64;
> > > > > > + s64 elapsed_msecs64;
> > > > > >
> > > > > > - elapsed_centisecs64 = timeval_to_ns(stop) - timeval_to_ns(start);
> > > > > > - do_div(elapsed_centisecs64, NSEC_PER_SEC / 100);
> > > > > > - return elapsed_centisecs64;
> > > > > > + elapsed_msecs64 = timeval_to_ns(stop) - timeval_to_ns(start);
> > > > > > + do_div(elapsed_msecs64, NSEC_PER_SEC / 1000);
> > > > > > + return elapsed_msecs64;
> > > > > > }
> > > > > >
> > > > > > static char *pm_verb(int event)
> > > > > > @@ -476,7 +476,7 @@ static char *pm_verb(int event)
> > > > > > static void dpm_show_time(struct timeval *start, struct timeval *stop,
> > > > > > pm_message_t state, const char *info)
> > > > > > {
> > > > > > - int centisecs = pm_time_elapsed(start, stop);
> > > > > > + int centisecs = pm_time_elapsed(start, stop) / 10;
> > > > > >
> > > > > > printk(KERN_INFO "PM: %s%s%s of devices complete in %d.%02d seconds\n",
> > > > > > info ? info : "", info ? " " : "", pm_verb(state.event),
> > > > > > @@ -497,6 +497,33 @@ static void pm_dev_err(struct device *de
> > > > > > kobject_name(&dev->kobj), pm_verb(state.event), info, error);
> > > > > > }
> > > > > >
> > > > > > +#ifdef DEBUG
> > > > > > +static void device_show_time(struct timeval *start, struct device *dev,
> > > > > > + pm_message_t state, char *info)
> > > > > > +{
> > > > > > + struct timeval stop;
> > > > > > + int msecs;
> > > > > > +
> > > > > > + do_gettimeofday(&stop);
> > > > > > + msecs = pm_time_elapsed(start, &stop);
> > > > > > + dev_dbg(dev, "PID %d: %s%s%s complete in %d.%03d seconds\n",
> > > > > > + task_pid_nr(current), info ? info : "", info ? " " : "",
> > > > > > + pm_verb(state.event), msecs / 1000, msecs % 1000);
> > > > > > +}
> > > > > > +
> > > > > > +#define TIMER_DECLARE(timer) struct timeval timer
> > > > > > +#define TIMER_START(timer) do { \
> > > > > > + do_gettimeofday(&timer); \
> > > > > > + } while (0)
> > > > > > +#define TIMER_STOP(timer, dev, state, info) do { \
> > > > > > + device_show_time(&timer, dev, state, info); \
> > > > > > + } while (0)
> > > > > > +#else /* !DEBUG */
> > > > > > +#define TIMER_DECLARE(timer)
> > > > > > +#define TIMER_START(timer) do { } while (0)
> > > > > > +#define TIMER_STOP(timer, dev, state, info) do { } while (0)
> > > > > > +#endif /* !DEBUG */
> > > > > > +
> > > > > > /*------------------------- Resume routines -------------------------*/
> > > > > >
> > > > > > /**
> > > > > > @@ -510,7 +537,9 @@ static void pm_dev_err(struct device *de
> > > > > > static int __device_resume_noirq(struct device *dev, pm_message_t state)
> > > > > > {
> > > > > > int error = 0;
> > > > > > + TIMER_DECLARE(timer);
> > > > > >
> > > > > > + TIMER_START(timer);
> > > > > > TRACE_DEVICE(dev);
> > > > > > TRACE_RESUME(0);
> > > > > >
> > > > > > @@ -523,6 +552,7 @@ static int __device_resume_noirq(struct
> > > > > > wake_up_all(&dev->power.wait_queue);
> > > > > >
> > > > > > TRACE_RESUME(error);
> > > > > > + TIMER_STOP(timer, dev, state, "EARLY");
> > > > > > return error;
> > > > >
> > > > > Hm, these CPP macros are rather ugly. Why is there a need for
> > > > > the TIMER_DECLARE() wrapper - if a proper inline function is
> > > > > used there's no need for that.
> > > >
> > > > I need a variable to be declared so that I can save the "start"
> > > > timestamp in it. I don't need the variable if DEBUG is unset,
> > > > though.
> > > >
> > > > How would you do that without using a macro? Or #ifdef #endif
> > > > block that would be uglier IMO (which is why I didn't do that)?
> > >
> > > Well, why not use an inline function like i suggested? [which does
> > > nothing in the !enabled case] You can keep the local variable always
> > > defined.
> >
> > Well, I used the macros _exactly_ because I didn't want to keep
> > the local variable always defined.
> >
> > Now, if you think that adding several useless bytes to the stack
> > frame is OK, perhaps it can be always defined. However, IMnsHO
> > that would be (a) confusing (why define a variable you don't use)
> > and (b) wasteful.
>
> Well the compiler will eliminate them, doesnt it?
If the compiler is guaranteed to eliminate them (without generating a "variable
defined but not used" warning for that matter), then they can be always
defined.
Thanks,
Rafael
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