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SubjectRe: [PATCH v5 1/1] serial/8250: Use fifo in 8250 console driver
On Fri, 1 Apr 2022 06:35:58 +0200
Jiri Slaby <jirislaby@kernel.org> 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.

-- Steve

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