Messages in this thread |  | | | Date | Fri, 16 Oct 2009 09:42:22 +0200 | | From | Ingo Molnar <> | | Subject | Re: [PATCH] perf tools: Add a new generic section in perf.data |
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> On Fri, Oct 16, 2009 at 09:10:46AM +0200, Ingo Molnar wrote: > > > > * Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > > > +/* > > > + * Version 0: contains trace_info section only > > > + */ > > > +struct perf_file_additionals { > > > + u64 version; > > > + struct perf_file_section trace_info; > > > +}; > > > > i dont disagree with the change - but it would be even nicer to simply > > define a features bitmask, instead of a flat version - and add the > > trace_info section as a feature. > > > > That way it's all a lot more manageable: we dont know about versions per > > se, we know about features. Individual features could be developed (and > > backported) in a distributed way - without having to worry about a flat > > version model. > > > > So i'd suggest something like a bitmask in the perf.data file header: > > > > DECLARE_BITMAP(features, 256); > > > > Plus every perf version knows about the features it supports: > > > > DECLARE_BITMAP(features_supported, 256); > > > > The compatibility rule is: perf only touches attributes that belong to > > features it knows about. > > > > Ingo > > > Yeah, I've thought about that too but feared about the limitation of > bitweight(u64), although it's probably enough, we never know. That > said I can take a bunch of four u64 to draw this bitmap and 256 > features is enough. > > Indeed that's way much better as a bitmap. Will do that instead.
Yeah, but please reuse linux/bitmap.h instead of some open-coded array of 4x u64's.
Ingo
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