Messages in this thread | | | Date | Wed, 4 Dec 2013 14:57:43 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/3] perf/x86/amd: AMD support for bp_len > HW_BREAKPOINT_LEN_8 |
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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.
> >> 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.
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.
Oleg.
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