On Mon, May 29, 2017 at 12:24:53PM +0300, Alexey Budankov wrote: > On 29.05.2017 10:45, Peter Zijlstra wrote: > > On Sat, May 27, 2017 at 02:19:51PM +0300, Alexey Budankov wrote: > > > Solution: > > > > > > cpu indexed trees for perf_event_context::pinned_groups and > > > perf_event_context::flexible_groups lists are introduced. Every tree node > > > keeps a list of groups allocated for the same cpu. A tree references only > > > groups located at the appropriate group list. The tree provides capability > > > to iterate over groups allocated for a specific cpu only, what is exactly > > > required by multiplexing timer interrupt handler. The handler runs per-cpu > > > and enables/disables groups using group_sched_in()/group_sched_out() that > > > call event_filter_match() function filtering out groups allocated for cpus > > > different from the one executing the handler. Additionally for every > > > filtered out group group_sched_out() updates tstamps values to the current > > > interrupt time. This updating work is now done only once by > > > update_context_time() called by ctx_sched_out() before cpu groups > > > iteration. For this trick to work it is required that tstamps of filtered > > > out events would point to perf_event_context::tstamp_data object instead > > > of perf_event::tstamp_data ones, as it is initialized from an event > > > allocation. tstamps references are switched by > > > group_sched_in()/group_sched_out() every time a group is checked for its > > > suitability for currently running cpu. When a thread enters some cpu on > > > a context switch a long run through pinned and flexible groups is > > > performed by perf_event_sched_in(, mux=0) with new parameter mux set to 0 > > > and filtered out groups tstamps are switched to > > > perf_event_context::tstamp_data object. Then a series of multiplexing > > > interrupts happens and the handler rotates the flexible groups calling > > > ctx_sched_out(,mux=1)/perf_event_sched_in(,mux=1) iterating over the cpu > > > tree lists only and avoiding long runs through the complete group lists. > > > This is where speedup comes from. Eventually when the thread leaves the > > > cpu > > > ctx_sched_out(,mux=0) is called restoring tstamps pointers to the events' > > > perf_event::tstamp_data objects. > > > > This is unreadable.. Please use whitespace. > > Do you mean do NOT use whitespaces? Could you explain in more detail what > you mean?
No, add _more_ whitespace. Use things like paragraphs and such. Reading a massive blob of text like that is painful. Also use full and complete sentences. For example, the very first sentence: 'cpu indexed trees for perf_event_context::pinned_groups and perf_event_context::flexible_groups lists are introduced.' feels incomplete and leaves one wondering what for etc.. And it only gets worse. > > Yeah, this doesn't go into a changelog. Have you _ever_ seen a changelog > > with such crud in? > > > > I have not. Could you please advise how to format this information to be > suitable for changelog, if it's required at all? Don't include it. It should be fairly obvious from the diff itself what changed after all.
