[Bugs] [Bug 1349953] thread CPU saturation limiting throughput on write workloads

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1349953



--- Comment #9 from Xavier Hernandez <xhernandez at datalab.es> ---
I'm not sure what is exactly happening here. Enabling client-io-threads should
not move the encoding load to the epoll threads for most of the requests.
However the decoding load should be done mainly by the epoll threads.

In your test you are doing writes, right ? in this case the epoll threads
should only be handling the answers, with no encoding/decoding.

2.78 GB/s in records of 64k means a total of 43.421 requests per second. A 4+2
EC volume multiplies this by 6, for a total of 260.526 requests of 16k per
second. On average, each client is receiving 43.421 answers per second
(assuming a balanced load). Could it be that the communications layer could not
handle so many answers ?

Having 4 epoll threads means each thread handles 10.855 requests/s, while 2
threads need to handle 21.711 requests/s. Not sure if this is too many or not.

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