> From: Mattias Rönnblom [mailto:mattias.ronnb...@ericsson.com] > Sent: Tuesday, 6 September 2022 18.14 > > As a part of its service function, a service usually polls some kind > of source (e.g., an RX queue, a ring, an eventdev port, or a timer > wheel) to retrieve one or more items of work. > > In low-load situations, the service framework reports a significant > amount of cycles spent for all running services, despite the fact they > have performed little or no actual work. > > The per-call cycle expenditure for an idle service (i.e., a service > currently without pending jobs) is typically very low. Polling an > empty ring or RX queue is inexpensive. However, since the service > function call frequency on an idle or lightly loaded lcore is going to > be very high indeed, the service function calls' cycles adds up to a > significant amount. The only thing preventing the idle services' > cycles counters to make up 100% of the available CPU cycles is the > overhead of the service framework itself. > > If the RTE_SERVICE_ATTR_CYCLES or RTE_SERVICE_LCORE_ATTR_CYCLES are > used to estimate service core load, the cores may look very busy when > the system is mostly doing nothing useful at all. > > This patch allows for an idle service to indicate that no actual work > was performed during a particular service function call (by returning > -EAGAIN). In such cases the RTE_SERVICE_ATTR_CYCLES and > RTE_SERVICE_LCORE_ATTR_CYCLES values are not incremented. > > The convention of returning -EAGAIN for idle services may in the > future also be used to have the lcore enter a short sleep, or reduce > its operating frequency, in case all services are currently idle. > > This change is backward-compatible. > > Signed-off-by: Mattias Rönnblom <mattias.ronnb...@ericsson.com> > ---
This entire series contains a bunch of good improvements. Returning -EAGAIN is a step in the right direction towards measuring CPU usage, and a great way to make it backwards compatible. Series-Acked-by: Morten Brørup <m...@smartsharesystems.com>
