Messages in this thread | | | Subject | RE: [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now) | From | Steven Rostedt <> | Date | Fri, 18 Feb 2011 15:36:35 -0500 |
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On Fri, 2011-02-18 at 15:10 -0500, Dominique Toupin wrote: > My understanding is stop_machine will stop all processors for many ms.
s/ms/us/
> Even if most of our systems are not hard real-time they are soft real-time and stopping all cores for a few ms is not allowed. > We can stop a few threads while we are jump patching but all processors is too much for us.
I think I could hit a single ms if we enable full function tracing which disables ~22,000 functions in one shot. But if you enable full function tracing, the kernel can slow down quite drastically, and that would even be more problematic than a single ms hic-up. As hackbench showed a %150 slowdown when function tracer was running.
Now the last measurements I took was a few years ago and it was on a 4 CPU box. Perhaps stop_machine() may be a bit more expensive on a 1024 CPU box.
-- Steve
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