> Hello,
> 
> > I used Youquan's patch, but we have noticed that it can only overcome soft
> > limits,
> > but not hard limits. E.g. on Fedora (and probably others) there is a soft
> > limit
> > of 1024 and a hard limit of 4096, so if powertop opens at least 15 file
> > descriptors
> > per CPU, then this will fail on a system with >273 CPUs.
> 
> that's a pretty big system
> 
> > In case you think we can also temporally increase the hard limit (as we
> > already have
> > the privilege), the attached patch will do it. In case you think the hard
> > limits set by
> > the system administrator are untouchable (e.g. violation of system
> > resources hard limits
> > could result in a bad effects like explosion in a nuclear power plant :),
> > the
> > previously sent patch that fixes the error message needs to be also used
> 
> hm, need to think about this for a moment. both your patches make sense.
> I'd probably go with `temporally increase the hard limit' solution, to make
> someones life easier. what do you, guys, think?
> 
> 
> 	-ss
> 
> > regards
> > 
> > Jaroslav
> 
> > diff --git a/src/main.cpp b/src/main.cpp
> > index 0883424..e0e8a71 100644
> > --- a/src/main.cpp
> > +++ b/src/main.cpp
> > @@ -36,6 +36,8 @@
> >  #include <getopt.h>
> >  #include <unistd.h>
> >  #include <locale.h>
> > +#include <sys/resource.h>
> > +#include <linux/limits.h>
> >  
> >  #include "cpu/cpu.h"
> >  #include "process/process.h"
> > @@ -283,11 +285,16 @@ static void powertop_init(void)
> >  	static char initialized = 0;
> >  	int ret;
> >  	struct statfs st_fs;
> > +	struct rlimit rlmt;
> >  
> >  	if (initialized)
> >  		return;
> >  
> >  	checkroot();
> > +
> > +	rlmt.rlim_cur = rlmt.rlim_max = NR_OPEN;

This seems to be wrong. On my system NR_OPEN is 1024, but
/proc/sys/fs/nr_open gives me 1048576. It seems the linux kernel
hardcodes 1024 * 1024 as the default kernel limit. This default
limit can be raised to:

sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
  -BITS_PER_LONG;

which is 2 Gi - 63 on my 64 bit system. I think we shouldn't
touch/increase this. It seems there is no header definition for these
limits.

I am proposing new patch, which reads the current kernel limit from the
/proc. I am not sure about the portability, but at least it shouldn't
break anything.

Finally I think, the first patch could be applied together with this patch
(probably with the changed message) to notify user that he/she reached
the FDs limit, because there is still some limit. This could also
occur if some process would decrease the /proc/sys/fs/nr_open after
it is read by powertop and before the ulimit is set

regards

Jaroslav