PING On Fri, Apr 19, 2013 at 1:30 PM, Janne Blomqvist <blomqvist.ja...@gmail.com> wrote: > Hi, > > the attached patch improves the performance for unformatted and > unbuffered files. Currently unbuffered unformatted really means that > we don't buffer anything and use the POSIX I/O syscalls directly. With > the patch, we use the buffer but flush it at the end of each I/O > statement. > > (For formatted I/O we essentially already do this, as the format > buffer (fbuf) buffers each record). > > For the ever important benchmark of writing small (containing a single > scalar 4 byte value) unformatted sequential records to /dev/null, the > patch reduces the number of syscalls by a factor of 6, and performance > improves by more than double. > > For trunk, time for the benchmark in the PR: > > real 0m0.727s > user 0m0.272s > sys 0m0.452s > > With the patch: > > real 0m0.313s > user 0m0.220s > sys 0m0.092s > > For comparison, writing to a file where we use buffered I/O: > > real 0m0.202s > user 0m0.180s > sys 0m0.020s > > > As a semi-unrelated minor improvement, the patch also changes the > ordering when writing out unformatted sequential record markers. > Currently we do > > write bogus marker > write record data > write tail marker > seek back to before the bogus marker > write the correct head marker > seek to the end of the record, behind the tail marker > > With the patch we instead do > > write bogus marker > write record data > seek back to before the bogus marker > write the correct head marker > seek to the end of the record data > write tail marker > > With the patch, the slightly shorter seek distances ever-so-slightly > increase the chance that the seeks will be contained within the buffer > so we don't have to flush. > > Regtested on x86_64-unknown-linux-gnu, Ok for trunk? > > 2013-04-19 Janne Blomqvist <j...@gcc.gnu.org> > > PR fortran/56981 > * io/transfer.c (next_record_w_unf): First fix head marker, then > write tail. > (next_record): Call flush_if_unbuffered. > * io/unix.c (struct unix_stream): Add field unbuffered. > (flush_if_unbuffered): New function. > (fd_to_stream): New argument. > (open_external): Fix fd_to_stream call. > (input_stream): Likewise. > (output_stream): Likewise. > (error_stream): Likewise. > * io/unix.h (flush_if_unbuffered): New prototype. > > > -- > Janne Blomqvist
-- Janne Blomqvist
