Messages in this thread | | | Date | Tue, 4 Nov 2008 09:07:47 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/3] ftrace: function tracer with irqs disabled |
| |
* Steven Rostedt <rostedt@goodmis.org> wrote:
> Running hackbench 3 times with the irqs disabled and 3 times with > the preempt disabled function tracer yielded: > > tracing type times entries recorded > ------------ -------- ---------------- > irq disabled 43.393 166433066 > 43.282 166172618 > 43.298 166256704 > > preempt disabled 38.969 159871710 > 38.943 159972935 > 39.325 161056510
your numbers might be correct, but i found that hackbench is not reliable boot-to-boot - it can easily produce 10% systematic noise or more. (perhaps depending on how the various socket data structures happen to be allocated)
the really conclusive way to test this would be to add a hack that either does preempt disable or irqs disable, depending on a runtime flag - and then observe how hackbench performance reacts to the value of that flag.
note that preempt-disable will also produce less trace entries, especially in very irq-rich workloads. Hence it will be "faster".
Ingo
| |