RE: [PATCH v2] Unbuffered output when pipe/tee to a file

[David Laight]

From: Arnaldo Carvalho de Melo
> Sent: 09 December 2021 18:51
...
> > diff --git a/tools/perf/tests/builtin-test.c b/tools/perf/tests/builtin-test.c
> > index 8cb5a1c3489e..d92ae4efd2e6 100644
> > --- a/tools/perf/tests/builtin-test.c
> > +++ b/tools/perf/tests/builtin-test.c
> > @@ -606,6 +606,9 @@ int cmd_test(int argc, const char **argv)
> >          if (ret < 0)
> >                  return ret;
> >
> > +	/* Unbuffered output */
> > +	setvbuf(stdout, NULL, _IONBF, 0);
> > +

You only want _IOLBF (line buffered).

Otherwise you are likely to get a lot of write() system calls.
Even multiple ones from the same printf().

Although it can be better just to ensure there is a fflush(stdout)
inside the loop.

	David

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