Messages in this thread |  | | Date | Tue, 10 Dec 2013 15:43:34 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 1/3] perf/x86/amd: AMD support for bp_len > HW_BREAKPOINT_LEN_8 |
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On Wed, Dec 04, 2013 at 02:57:43PM +0100, Oleg Nesterov wrote: > On 12/03, Frederic Weisbecker wrote: > > > > 2013/11/11 Oleg Nesterov <oleg@redhat.com>: > > > On 11/11, Frederic Weisbecker wrote: > > >> > > >> On Sat, Nov 09, 2013 at 04:54:28PM +0100, Oleg Nesterov wrote: > > >> > > > >> > Up to you and Suravee, but can't we cleanup this later? > > >> > > > >> > This series was updated many times to address a lot of (sometimes > > >> > contradictory) complaints. > > >> > > >> Sure. But I'm confident that we can solve the conflicting mask / len issue easily beside. > > >> I mean, I don't feel confident with merging things as is, otoh it should be easy to fix up. > > > > > > I do not really understand where do you see the conflict... > > > > > > I can be easily wrong, but afaics currently mask / len issue is simply > > > the implementation detail. > > > > I think it's like we have an object that has a length, and to create > > this object we pass both kilometers and miles. Ok it's a bit different > > here because a mask can apply on top of a len. But here it's used to > > define essentially the same thing (ie: a range of address) > > Yes. perf/etc uses length, the current imlementation uses ->mask to > actually set the range. > > > > Actually, mask is more powerfull. And initial versions of this patches > > > (iirc) tried to use mask as an argument which comes from the userspace > > > (tools/perf, perf_event_attr, etc). But one of reviewers nacked this > > > interfacer, so we still use len. > > > > Well, we can still reconsider it if needed but to me it seems that > > mask is only interesting if we may deal with non contiguous range of > > addresses. > > And this is what this mask can actually do. Just there is no way (currently) > to pass the mask from userpace.
Ok but are we interested in non contiguous range?
> > > >> Right but what if we want breakpoints having a size below 8? Like break on instructions > > >> from 0x1000 to 0x1008 ? > > >> > > >> Or should we ignore range instruction breakpoints when len < 8? > > > > > > In this case the new code has no effect (iirc), we simply use > > > X86_BREAKPOINT_LEN_* and "tell the hardware about extended range/mask" > > > code is never called. IIRC, currently we simply check bp_mask != 0 > > > to distinguish. > > > > I'm not sure I understand correctly. Do you mean that range below 8 > > don't rely on extended breakpoint range? > > IIRC - yes. > > > Ideally it would be nice if we drop bp_mask and use extended ranges > > only when len > 8. How does that sound? > > Again, iirc, this is what the code does. except (in essence) it checks > mask != 0 instead of len > 8.
Ok.
> > And yes, we can probably drop bp_mask (unless we are going to support > the contiguous ranges), just I think we can do this later.
The problem is that once we push the bp_mask interface, we won't be able to remove it later. It's a user ABI.
So I really want to be careful with that and extend bp_len for range breakpoints then if we find out limitations, only then we can introduce bp_mask.
Suravee, any thought about this?
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