New Layer “Waiting for CPU” improves on “Unaccounted Wait”

Since Tideways PHP extension 5.17.0 the time spent in the “runqueue” is tracked, waiting for the CPU scheduler to continue the current process.

This improves the layer calculation of Tideways to explain a good part of what previously was tracked as “Unaccounted Wait” time.

The trace summary now includes this new metric and gives you an indication when the server have too much going on at the same time, meaning that the CPU cores have to put PHP processes to sleep for longer amounts of time because of too many running in parallel.

Like in this example where “Waiting for CPU” accounts for 225ms of the request.