[Pdbg] [PATCH 7/7] pdbg/htm: Enforce powersave=off

[Michael Neuling]

On Fri, 2018-03-16 at 14:06 +1100, Cyril Bur wrote:
> On Fri, 2018-03-16 at 13:53 +1100, Michael Neuling wrote:
> > Why not just use the sysfs interface to turn off the cpuidle driver?
> > 
> 
> I can add that as another hint to the user. It isn't pdbgs place to
> change the state of the system but providing the most user friendly
> hints is!

ok. FWIW, this will do it:

  for i in /sys/devices/system/cpu/cpu*/cpuidle/state*/disable ; do echo 1 > $i ; done

Mikey

> > Mikey
> > 
> > 
> > On Wed, 2018-03-07 at 16:49 +1100, Cyril Bur wrote:
> > > Core HTM has a nasty habit of not working if the stars haven't aligned
> > > with the exact polar axis of Mars. To complicate matters if Zeus got up
> > > on the incorrect side of the bed Core HTM will likely reflect his mood.
> > > 
> > > Core HTM requires that no threads be in powersave. It isn't clear if
> > > this restriction only applies to threads on the core being traced on or
> > > if this is a global thing. In order to be as safe as possible, pdbg
> > > will enforce that powersave be disabled globally.
> > > 
> > > Signed-off-by: Cyril Bur <cyrilbur at gmail.com>
> > > ---
> > > Initially I thought we would also have to mandate `ppc64_cpu --smt=off`
> > > because other tools do it. Some thinking later it doesn't make sense to
> > > enforce that, really the only thing we have to do with respect to Linux
> > > is powersave=off, having a sleeping thread while core trace is
> > > guaranteed to do bad things. I have a feeling that other tools got a
> > > bit confused between powersave and smt (at least the Linux view of both).
> > > 
> > > It works on a Palmetto with `ppc64_cpu --smt=8`. I am waiting on
> > > confirmation that the resulting trace is sane but I don't have any
> > > reason to believe it isn't
> > > ---
> > >  src/htm.c | 37 ++++++++++++++++++++++++++++++++++++-
> > >  1 file changed, 36 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/src/htm.c b/src/htm.c
> > > index 1032a5c..4917d1a 100644
> > > --- a/src/htm.c
> > > +++ b/src/htm.c
> > > @@ -259,6 +259,7 @@ static void print_usage(enum htm_type type)
> > >  
> > >  int run_htm(int optind, int argc, char *argv[])
> > >  {
> > > +	struct pdbg_target *target;
> > >  	enum htm_type type;
> > >  	int i, rc = 0;
> > >  
> > > @@ -278,9 +279,43 @@ int run_htm(int optind, int argc, char *argv[])
> > >  		return 0;
> > >  	}
> > >  
> > > -	if (type == HTM_CORE)
> > > +	if (type == HTM_CORE) {
> > >  		fprintf(stderr, "Warning: Core HTM is currently
> > > experimental\n");
> > >  
> > > +		/*
> > > +		 * Check that powersave is off.
> > > +		 *
> > > +		 * This is as easy as checking that every single
> > > +		 * thread is "ACTIVE" and hasn't gone into any sleep
> > > +		 * state.
> > > +		 */
> > > +		pdbg_for_each_class_target("thread", target) {
> > > +			if (pdbg_target_status(target) ==
> > > PDBG_TARGET_NONEXISTANT)
> > > +				continue;
> > > +
> > > +			if ((thread_status(target) &
> > > THREAD_STATUS_ACTIVE) !=
> > > THREAD_STATUS_ACTIVE) {
> > > +				fprintf(stderr, "It appears powersave is
> > > on
> > > 0x%"  PRIx64 "%p\n", thread_status(target), target);
> > > +				fprintf(stderr, "core HTM needs to run
> > > with
> > > powersave off\n");
> > > +				fprintf(stderr, "Hint: put powersave=off
> > > on
> > > the kernel commandline\n");
> > > +				return 0;
> > > +			}
> > > +		}
> > > +
> > > +		i = 0;
> > > +		pdbg_for_each_class_target("core", target)
> > > +			if (!target_is_disabled(target))
> > > +				i++;
> > > +		if (i == 0)
> > > +			fprintf(stderr, "You haven't selected any HTM
> > > Cores\n");
> > > +		if (i > 1) {
> > > +			fprintf(stderr, "It doesn't make sense to core
> > > trace
> > > on"
> > > +				" multiple cores at once. %d\n", i);
> > > +			fprintf(stderr, "What you probably want is -p 0
> > > -c
> > > x\n");
> > > +		}
> > > +		if (i != 1)
> > > +			return 0;
> > > +	}
> > > +
> > >  	optind++;
> > >  	for (i = 0; i < ARRAY_SIZE(actions); i++) {
> > >  		if (strcmp(argv[optind], actions[i].name) == 0) {
> > > -- 
> > > 2.16.2
> > > 
> 
>