Messages in this thread | | | Date | Tue, 7 Jan 2014 09:38:03 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow tracing units |
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On Mon, Jan 06, 2014 at 03:10:28PM -0800, Andi Kleen wrote: > Peter Zijlstra <peterz@infradead.org> writes: > > Also, do clarify the other points I asked about. Esp. the non > > FREEZE_ON_PMI behaviour of the PT PMI is worrying me immensely. > > The only reason for hardware freeze is when you have a few entries (like > with LBRs) so the interrupt entry code could overwhelm it. > > But PT is not small, it's gigantic: even with the smallest buffer you > have many thousands of entries. > > So you will get a few branches in the interrupt entry, but it's not a problem > because everything you really wanted to trace is still there. > > Eventually the handler disables PT, so there's no risk of racing with > the update or anything like that. > > Did I miss anything?
Yes; go read this:
lkml.kernel.org/r/20131219125205.GT3694@twins.programming.kicks-ass.net
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