Em Sat, Oct 27, 2018 at 08:58:30PM -0700, David Miller escreveu: > > If I run perf top with a "make -j128" kernel build, I get ring buffer event > processing timeouts which results in: > > ui__warning("Too slow to read ring buffer.\n" > "Please try increasing the period (-c) or\n" > "decreasing the freq (-F) or\n" > "limiting the number of CPUs (-C)\n"); > > from perf_top__mmap_read(). > > This hangs the main event thread. Only the display thread runs after > this point. > > We can't issue UI messages from the event thread, because those will > hang waiting for a keypress. The display thread will eat any keys > we press and the event thread thus hangs forever. > > I can tell this is what has happened because the histogram entries > continue to decay, yet the event count stops increasing. > > If I put a gdb on the perf process, indeed the backtrace in the event > processing thread is in the select() call done by ui__getch(). > > Adding insult to injury, the display thread immediately overwrites the > warning message printed by the event thread, and thus the user has no > chance to even see it. > > I really wonder how this was tested. > > Perhaps we should mark the event thread in a special way and trigger > assertions if UI messages are printed from it. Again, any such > operation will hang the thread and stop all event processing.
Right, I thought about marking a flag in the main event thread that then gets picked up by the display thread, I'll try and write a patch for that, if none has been submitted, I'm still downloading this weekend's messages. - Arnaldo P.S. I was busy working as a volunteer in the brazilian elections :-\