IPI Benchmark Data?
merritt.alex at gmail.com
Thu Aug 4 16:32:00 PDT 2016
That's awesome, thanks for sharing. For the Broadwell system, it seems to
take 2-3 microseconds in C-state 1. By any chance do you have numbers for
C-state 0? I am curious what an IPI costs for a non-idle cpu, too. These
numbers are interesting, though, I didn't realize wake-ups cost so much (or
to think about whether to send an IPI to an idle core in the first place).
If cpu #16 is the neighbor SMT thread for cpu #0, wouldn't IPI latencies be
minimal? I assumed both SMT threads couldn't be in different C-states since
they share resources. Unless I am reading the data incorrectly...
On Wed, Aug 3, 2016 at 12:29 PM, Matthew Dillon <dillon at backplane.com>
> I have some saved output from ./ipitest script runs that I've run on
> various cpus:
> The numbers are in nanoseconds, so e.g. '2900' would be 2.9uS. '29000'
> would be 29uS. The originating cpu is #0. As an example, taking
> ipitest05.txt, due to the topological layout cpu #16 is the co-thread for
> cpu #0 and one can see it in the numbers (since cpu #0 is initiating the
> test, it's generally not running in a low-power mode regardless of the C
> state we use).
> The results generally follow expectations. A cpu sitting in a deep C
> state can take over 30uS to respond. Minimum IPI latency is usually in the
> 1-2uS range.
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