Messages in this thread | | | Date | Fri, 7 Apr 2017 19:20:24 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 2/5] perf/x86/intel: Record branch type |
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On Fri, Apr 07, 2017 at 09:48:34AM -0700, Andi Kleen wrote: > On Fri, Apr 07, 2017 at 05:20:31PM +0200, Peter Zijlstra wrote: > > On Fri, Apr 07, 2017 at 06:47:43PM +0800, Jin Yao wrote: > > > Perf already has support for disassembling the branch instruction > > > and using the branch type for filtering. The patch just records > > > the branch type in perf_branch_entry. > > > > > > Before recording, the patch converts the x86 branch classification > > > to common branch classification and compute for checking if the > > > branches cross 4K or 2MB areas. It's an approximate computing for > > > crossing 4K page or 2MB page. > > > > The changelog is completely empty of rationale. Why do we care? > > > > Not having the binary is a very bad reason; you can't do much of > > anything if that's missing. > > It's a somewhat common situation with partially JITed code, if you > don't have an agent. You can still do a lot of useful things.
Like what? How can you say anything about code you don't have?
> We found it useful to have this extra information during workload > analysis. Forward conditionals and page crossing jumps > are indications of frontend problems.
But you already have the exact same information in {to,from}, why would you need to repackage information already contained?
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