Messages in this thread | | | Date | Sat, 4 Oct 2008 16:05:06 +1000 | From | David Gibson <> | Subject | Re: perfmon3 interface overview |
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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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