On Sat, 2 May 2026 18:17:06 -0400 Steven Rostedt <[email protected]> wrote:
> On Sat, 2 May 2026 15:23:04 -0400 > Steven Rostedt <[email protected]> wrote: > > > Hi Masami, > > > > I applied your patches and enabled your ptracingtest code. I noticed > > that when there's dropped pages, the trace output is not in order: > > > > # trace-cmd start -B ptracingtest -e all -v -e '*lock*' > > # taskset -c 5 echo c > /proc/sysrq-trigger > > > > On reboot, I ran: > > > > # trace-cmd show -B ptracingtest > /tmp/trace.out > > > > Then executed the attached perl program: > > > > # ./read-ts.pl < /tmp/trace.out > > > > And it errors our: > > > > 30.212495 < 30.213534 > > <...>-1048 [005] d.... 30.212495: irq_enable: > > caller=irqentry_exit+0xf5/0x710 parent=0x0 > > > > That is, I think the zero timestamps may be messing with the order. > > > > Ah, I think I found the problem. The iterator needs the same logic you > added for the consuming read: > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 7bfbed0ac90c..90a7fa772fe3 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -6105,12 +6105,14 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts) > struct ring_buffer_per_cpu *cpu_buffer; > struct ring_buffer_event *event; > int nr_loops = 0; > + int max_loops; > > if (ts) > *ts = 0; > > cpu_buffer = iter->cpu_buffer; > buffer = cpu_buffer->buffer; > + max_loops = cpu_buffer->ring_meta ? cpu_buffer->nr_pages : 3; > > /* > * Check if someone performed a consuming read to the buffer > @@ -6133,7 +6135,7 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts) > * the ring buffer with an active write as the consumer is. > * Do not warn if the three failures is reached. > */ > - if (++nr_loops > 3) > + if (++nr_loops > max_loops) > return NULL; > > if (rb_per_cpu_empty(cpu_buffer)) > > > I'll test this some more, and make a proper patch. Ah, indeed. Thanks for fixing! BTW, shouldn't we unify common logic of those functions? Thank you, > > -- Steve > -- Masami Hiramatsu (Google) <[email protected]>
