On Fri, Apr 26, 2013 at 05:20:44PM +0100, Will Deacon wrote: > Hi Jacob, > > On Fri, Apr 26, 2013 at 12:19:11AM +0100, Jacob Shin wrote: > > On Thu, Apr 25, 2013 at 10:17:35AM -0700, H. Peter Anvin wrote: > > > On 04/25/2013 10:06 AM, Oleg Nesterov wrote: > > > >> > > > >> The downside is that in userland perf tool we need differing > > > >> documentation > > > >> on what the mask syntax means for each architecture. > > > > > > > > Personally I think this is acceptable. > > > > > > > > But I am new to this code, so... > > > > > > > > > > That would seem really, really awkward. Yes, perf has a bunch of > > > low-level stuff, but it would seem highly undesirable to force the user > > > to deal with something like that. > > > > > > It would be good to have a user-friendly syntax that covers most of what > > > users may want to do and perhaps a longer form that can express > > > everything including ARM's byte selects; if the system can't honor the > > > request it should return an error. > > > > Okay, > > > > If arch specific masks are a no go, then I think I'm convinced that > > Oleg's idea of using bp_len is the right thing to do. Right now perf > > userland tool hard codes bp_len to 4, so I need to modify it to allow > > user to override the length if desired. > > So what value ends up in the bp_len field: a length or a mask? I just want > to make sure it's flexible enough that, if we add another user interface for > the byte-select stuff, we don't need to butcher the attr in another way.
It is length. Just as it is today, userland API does not change at all. > > > Oleg, Frederic, et al. > > > > Which syntax do you prefer? > > > > If we want to set bp_len to 16: > > > > $ perf stat -e mem:0x1000:rw:16 > > > > Or > > > > $ perf stat -e mem:0x1000:16 > > > > Or > > > > $ perf stat -e mem:0x1000/16 > > > > If no bp_len value is specified, it will still default to 4 as it did > > before. > > I certainly like the ability to change the length of an execute breakpoint, > as that helps for halfword instructions on ARM (not sure if your first > syntax precludes that, but just checking...). All three are equivalent, I just need to pick one and implement/document. -Jacob -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
