194ec34184
The function graph tracer replaces the return address with a hook to trace the exit of the function call. This hook will finish by returning to the real location the function should return to. But the current implementation uses a ret to jump to the real return location. This causes a imbalance between calls and ret. That is the original function does a call, the ret goes to the handler and then the handler does a ret without a matching call. Although the function graph tracer itself still breaks the branch predictor by replacing the original ret, by using a second ret and causing an imbalance, it breaks the predictor even more. This patch replaces the ret with a jmp to keep the calls and ret balanced. I tested this on one box and it showed a 1.7% increase in performance. Another box only showed a small 0.3% increase. But no box that I tested this on showed a decrease in performance by making this change. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: Frederic Weisbecker <fweisbec@gmail.com> LKML-Reference: <20091013203425.042034383@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu> |
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