[ Added Tom ] On Thu, 5 Sep 2019 09:03:01 -0700 Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > On Thu, Sep 5, 2019 at 7:43 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > [Add Steven] > > > > On Wed 04-09-19 12:28:08, Joel Fernandes wrote: > > > On Wed, Sep 4, 2019 at 11:38 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > On Wed 04-09-19 11:32:58, Joel Fernandes wrote: > > [...] > > > > > but also for reducing > > > > > tracing noise. Flooding the traces makes it less useful for long traces and > > > > > post-processing of traces. IOW, the overhead reduction is a bonus. > > > > > > > > This is not really anything special for this tracepoint though. > > > > Basically any tracepoint in a hot path is in the same situation and I do > > > > not see a point why each of them should really invent its own way to > > > > throttle. Maybe there is some way to do that in the tracing subsystem > > > > directly. > > > > > > I am not sure if there is a way to do this easily. Add to that, the fact that > > > you still have to call into trace events. Why call into it at all, if you can > > > filter in advance and have a sane filtering default? > > > > > > The bigger improvement with the threshold is the number of trace records are > > > almost halved by using a threshold. The number of records went from 4.6K to > > > 2.6K. > > > > Steven, would it be feasible to add a generic tracepoint throttling? > > I might misunderstand this but is the issue here actually throttling > of the sheer number of trace records or tracing large enough changes > to RSS that user might care about? Small changes happen all the time > but we are likely not interested in those. Surely we could postprocess > the traces to extract changes large enough to be interesting but why > capture uninteresting information in the first place? IOW the > throttling here should be based not on the time between traces but on > the amount of change of the traced signal. Maybe a generic facility > like that would be a good idea? You mean like add a trigger (or filter) that only traces if a field has changed since the last time the trace was hit? Hmm, I think we could possibly do that. Perhaps even now with histogram triggers? -- Steve
