On Fri, Jul 13, 2018 at 3:49 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > On Fri, Jul 13, 2018 at 03:13:07PM -0700, Suren Baghdasaryan wrote: >> On Thu, Jul 12, 2018 at 10:29 AM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote: >> > might want to know about and react to stall states before they have >> > even concluded (e.g. a prolonged reclaim cycle). >> > >> > This patches the procfs/cgroupfs interface such that when the pressure >> > metrics are read, the current per-cpu states, if any, are taken into >> > account as well. >> > >> > Any ongoing states are concluded, their time snapshotted, and then >> > restarted. This requires holding the rq lock to avoid corruption. It >> > could use some form of rq lock ratelimiting or avoidance. >> > >> > Requested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> >> > Not-yet-signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> >> > --- >> >> IMHO this description is a little difficult to understand. In essence, >> PSI information is being updated periodically every 2secs and without >> this patch the data can be stale at the time when we read it (because >> it was last updated up to 2secs ago). To avoid this we update the PSI >> "total" values when data is being read. > > That fix I actually folded into the main patch. We now always update > the total= field at the time the user reads to include all concluded > events, even if we sampled less than 2s ago. Only the running averages > are still bound to the 2s sampling window. > > What this patch adds on top is for total= to include any *ongoing* > stall events that might be happening on a CPU at the time of reading > from the interface, like a reclaim cycle that hasn't finished yet. Ok, I see now what you mean. So ondemand flag controls whether *ongoing* stall events are accounted for or not. Nit: maybe rename that flag to better explain it's function?
