On Fri, Apr 1, 2022 at 1:12 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Fri, 1 Apr 2022 06:35:58 +0200 > Jiri Slaby <jirislaby@xxxxxxxxxx> wrote: > > > > With the help of the function tracer, I then noticed the serial > > > controller was taking around 410us seconds to dispatch one single byte: > > > > > > $ trace-cmd record -p function_graph -g serial8250_console_write \ > > > ./sertest -n 1 /tmp/serco > > > > > > $ trace-cmd report > > > > > Note, the function graph tracer can add a noticeable amount of overhead to > these timings. If you want a more accurate time for a function, just trace > that one function: > > trace-cmd record -p function_graph -l serial8250_console_write ... > > As that will only trace the serial8250_console_write() function (think of > -l as "limit"), and the overhead of function graph for tracing a single > function becomes negligible, and then you can see the true time of that > function. > Thanks for the tip. I used bpftrace as a low overhead tracer. Then I used the function-graph tracer to get the details. > -- Steve >
