On Thu, Feb 29, 2024 at 9:23 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote: > > On Wed, Feb 28, 2024 at 01:19:12PM -0800, Namhyung Kim wrote: > > On Wed, Feb 28, 2024 at 12:16 PM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote: > > > On Wed, Feb 28, 2024 at 12:01:55PM -0800, Namhyung Kim wrote: > > > > On Wed, Feb 28, 2024 at 4:22 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote: > > > > > On Tue, Feb 27, 2024 at 09:33:35PM -0800, Namhyung Kim wrote: > > > > > > Currently it accounts the contention using delta between timestamps in > > > > > > lock:contention_begin and lock:contention_end tracepoints. But it means > > > > > > the lock should see the both events during the monitoring period. > > > > > > > Actually there are 4 cases that happen with the monitoring: > > > > > > > monitoring period > > > > > > / \ > > > > > > | | > > > > > > 1: B------+-----------------------+--------E > > > > > > 2: B----+-------------E | > > > > > > 3: | B-----------+----E > > > > > > 4: | B-------------E | > > > > > > | | > > > > > > t0 t1 > > > > > > > where B and E mean contention BEGIN and END, respectively. So it only > > > > > > accounts the case 4 for now. It seems there's no way to handle the case > > > > > > 1. The case 2 might be handled if it saved the timestamp (t0), but it > > > > > > lacks the information from the B notably the flags which shows the lock > > > > > > types. Also it could be a nested lock which it currently ignores. So > > > > > > I think we should ignore the case 2. > > > > > > Perhaps have a separate output listing locks that were found to be with > > > > > at least tE - t0 time, with perhaps a backtrace at that END time? > > > > > Do you mean long contentions in case 3? I'm not sure what do > > > > you mean by tE, but they started after t0 so cannot be greater > > > > case 2 > > > > monitoring period > > > / \ > > > | | > > > 2: B----+-------------E | > > > | | | > > > t0 tE t1 > > > > > > We get a notification for event E, right? We don´t have one for B, > > > because it happened before we were monitoring. > > > > Ah, ok. But there should be too many events in case 2 and > > I don't think users want to see them all. And they don't have > > So maybe a summary, something like: > > N locks that were locked before this session started have been > released, no further info besides this histogram of in-session > durations: > > 0-N units of time: ++ > N+1-M units of time: ++++ > ... Summary could work. But I'm not sure about the histogram since different locks would have different behavior - spinlock vs. mutex/semaphore. Maybe it's more meaningful when you have filters or separate histograms for each lock. > > > flags. But maybe we can update the flag when it sees exactly > > the same callstack later. > > The callstack, if going all the way to userspace may have the workload > targeted in the command line ( some pid, tid, CPU, etc) and thus would > point for things the user probably is interested than some other lock > that may affect it but indirectly. It doesn't collect user callstacks yet since it requires recording memory address space information of every process - basically FORK and MMAP. Maybe we can use callstacks with build-ID and offsets but it also requires mapping from build-ID to binary somewhere. Anyway, it's good to add more features to it. Let me process this patch first and think about more later. :) Thanks, Namhyung
