On Tue, Oct 16, 2018 at 09:42:04AM -0400, Steven Rostedt wrote: > > Joel, > > Can you Ack this patch. I want to push it upstream as without it, your > preemptirq latency test fails on one of my boxes. Causing my automated > tests to fail (I get by with removing the test from the automation). > > -- Steve > > > On Tue, 16 Oct 2018 09:40:05 -0400 > Steven Rostedt <[email protected]> wrote: > > > From: "Steven Rostedt (VMware)" <[email protected]> > > > > The preemptirq_delay_test module is used for the ftrace selftest code that > > tests the latency tracers. The problem is that it uses ktime for the delay > > loop, and then checks the tracer to see if the delay loop is caught, but the > > tracer uses trace_clock_local() which uses various different other clocks to > > measure the latency. As ktime uses the clock cycles, and the code then > > converts that to nanoseconds, it causes rounding errors, and the preemptirq > > latency tests are failing due to being off by 1 (it expects to see a delay > > of 500000 us, but the delay is only 499999 us). This is happening due to a > > rounding error in the ktime (which is totally legit). The purpose of the > > test is to see if it can catch the delay, not to test the accuracy between > > trace_clock_local() and ktime_get(). Best to use apples to apples, and have > > the delay loop use the same clock as the latency tracer does. > > > > Cc: Joel Fernandes (Google) <[email protected]> > > Cc: [email protected] > > Fixes: f96e8577da102 ("lib: Add module for testing preemptoff/irqsoff > > latency tracers") > > Signed-off-by: Steven Rostedt (VMware) <[email protected]>
Looks good to me! Acked-by: Joel Fernandes (Google) <[email protected]> thanks, - Joel
