RE: [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this isfor x86_64 right now)

[Steven Rostedt]

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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