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SubjectRe: perfmon3 interface overview
On Fri, Oct 03, 2008 at 01:12:09PM +0200, stephane eranian wrote:
> David,
> >> [snip]
> >> > III) attaching and detaching
> >> >
> >> > With v2.81:
> >> > int pfm_load_context(int fd, pfarg_load_t *load);
> >> > int pfm_unload_context(int fd);
> >> >
> >> > With v3.0:
> >> > int pfm_attach_session(int fd, int flags, int target);
> >> > int pfm_detach_session(int fd, int flags);
> >>
> >> Couldn't you get rid of one more syscall here by making detach a
> >> special case of attach with a special "null" value for target, or a
> >> special flag?
> >
> >
> > We could combine the two and use the flag field to indicate attach/detach.
> > The target is not a pointer but an int. Some people suggested I use an
> > unsigned long instead. In anycase, we could not use 0 to indicate "detach"
> > because CPU0 is a valid choice for system-wide. Thus we would have to
> > pick another value to mean "nothing", e.g, -1.
> >
> > > IV) starting and stopping
> > >
> > > With v2.81:
> > > int pfm_start(int fd, pfarg_start_t *st);
> > > int pfm_stop(int fd);
> > > int pfm_restart(int fd);
> > >
> > > With v3.0:
> > > int pfm_start_session(int fd, int flags);
> > > int pfm_stop_session(int fd, int flags);
> >
> >> Likewise, couldn't you cut this down by one more syscall by making it
> >> int pfm_set_session_state(int fd, int flags);
> >> and having a 'RUNNING' flag, which selects start or stop behaviour?
> >
> > That one we can certainly do. That's a good idea.
>
> Some more thoughts on this.
>
> If we wanted to go even further, we could combine start/stop, attach/detach
> into a single syscall:

Well, you could. But the attach/detach take a parameter which
start/stop don't, making it a less obvious merge to make.

> int pfm_control_session(int fd, int flags, int target);
> With flags:
> PFM_CTFL_START : start monitoring
> PFM_CTFL_STOP : stop monitoring
> PFM_CTFL_RESTART: resume after overflow notification
>
> PFM_CTFL_ATTACH: attach to thread or cpu designated by 'target'
> PFM_CTFL_DETACH: detach session
>
> But then, this is a form of ioctl() which people don't like....

--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson


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