On Fri, Sep 23, 2016 at 10:19:43AM -0700, Andi Kleen wrote: > On Fri, Sep 23, 2016 at 01:49:17PM +0200, Peter Zijlstra wrote: > > On Fri, Sep 23, 2016 at 02:27:20PM +0300, Alexander Shishkin wrote: > > > Hi Peter, > > > > > > This is an RFC, I'm not sending the tooling bits in this series, > > > although they can be found here [1]. > > > > > > This series introduces AUX data sampling for perf events, which in > > > case of our instruction/branch tracing PMUs like Intel PT, BTS, CS > > > ETM means execution flow history leading up to a perf event's > > > overflow. > > > > This fails to explain _WHY_ this is a good thing to have. What kind of > > analysis does this enable, and is that fully implemented in [1] (I > > didn't look). > > Think of it as a super LBR. (Near) all things LBR can do, PT can do > with much more branches for each sample.
Clarify the 'near'? Should we then not expose it as a BRANCH_STACK? Expand on the down-sides of that. > Also long term execution recording of PT normally doesn't work well because > the > sustained bandwidth is too high for perf and the disk to keep up > > Currently the main solution we have for that is the snapshot mode, but it > requires explicit instrumentation for someone to trigger snapshots. > > Sampling PT is an alternative that works for many use cases, and does > not rely on instrumentation. List a few use-cases on either side of that divide ? This really isn't rocket science, patches should come with justification, try and sell this stuff. Don't try and skimp on that.
