Messages in this thread |  | | | Date | Thu, 12 Jun 2008 18:10:55 -0400 | | From | Mathieu Desnoyers <> | | Subject | Re: Kernel marker has no performance impact on ia64. |
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* Peter Zijlstra (peterz@infradead.org) wrote: > On Thu, 2008-06-12 at 12:43 -0400, Frank Ch. Eigler wrote: > > > This is another reason why markers are a nice solution. They allow > > passing of actual useful values: not just the %p pointers but the most > > interesting derived values (e.g., prev->pid). > > Useful to whoem? stap isn't the holy grail of tracing and certainly not > the only consumer of trace points, so restricting the information to > just what stap needs is actually making trace points less useful. >
LTTng also currently relies on the markers identifying useful data and ideally won't contain any tracepoint-specific code to extract subfields from structures.
By the way, a point that should be clarified is that putting a "prev->pid" field in a marker does not make this variable live unless the marker is activated. When disabled, the marker site jumps over the stack setup, including any pointer dereference.
Mathieu
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