Messages in this thread | | | Date | Tue, 7 Oct 2014 17:25:28 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V5 14/16] perf, x86: enable LBR callstack when recording callchain |
| |
On Tue, Oct 07, 2014 at 03:00:43AM +0000, Liang, Kan wrote: > > > > > > On Wed, Sep 10, 2014 at 10:09:11AM -0400, kan.liang@intel.com wrote: > > > From: Kan Liang <kan.liang@intel.com> > > > > > > If a task specific event wants user space callchain but does not want > > > branch stack sampling, enable the LBR call stack facility implicitly. > > > The LBR call stack facility can help perf to get user space callchain > > > in case of there is no frame pointer. > > > > > > Note: this feature only affects how to get user callchain. The kernel > > > callchain is always got by frame pointers. > > > > Yeah, don't like this either. Suppose you have sane userspace (with > > framepointers enabled) then you're now loosing the better option. > > FP is the first option. This patch tries to enable LBR call stack facility implicitly. > Only when FP disabled or failed, we try to use LBR call stack. > Please refer to the previous patch https://lkml.org/lkml/2014/9/10/376
Still makes for an entirely unpredictable situation. That way you never quite know where your data came from.
| |