Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Dec 11, 2015 at 11:11:48AM -0700, Mathieu Poirier wrote:
> On 11 December 2015 at 06:36, Alexander Shishkin

> >  /**
> > + * Instruction trace (ITRACE) filter
> > + */
> > +struct perf_itrace_filter {
> > +       struct list_head        entry;
> > +       struct rcu_head         rcu_head;
> > +       struct inode            *inode;
> > +       struct task_struct      *task;
> > +       unsigned long           offset;
> > +       unsigned long           size;
> > +       unsigned long           start;
> > +       unsigned long           end;
> > +       unsigned int            range   : 1, /* 1: range, 0: addr */
> > +                               filter  : 1, /* 1: filter/start, 0: stop */
> > +                               kernel  : 1; /* 1: kernel, 0: object file*/
> 
> I've seen a rant on the list before about bit fields like these... Do
> we gain anything with having them?  I personally avoid them to favour
> bool types but that will be for Peter to decide.  Given its
> importance, I also think this structure could you more documentation.

Bool doesn't have a well defined storage type (although the x86_64 ABI
defines one, the language itself does not), so I tend to shy away from
using it in structures since its very hard to tell what the layout will
be.

Agreed on the comments though.