[bitbake-devel] [PATCH] siggen: Remove fsync that is causing performance issues

[Richard Purdie]

This fsync was added for belt and braces protection for things like sstate
on NFS. To be honest, it probably doesn't buy much, if the rename isn't
atomic, all bets are off anyway and there are bigger issues to worry about.

The issue is that at the end of every task, the dump_sig() code is triggered
to save out information about the task and this was triggering an fsync(fd).

Whilst it may select the file descriptor, on file systems like ext4, it will
require large parts of the journal to be written out so it can have
significant impact. latencytop showed an average fsync() call overhead of about
2s and if that happens for 5000 tasks, the time mounts up. This blocks the next
task execution by that time.

We therefore drop the fsync since in reality its causing problems and is unlikely
to buy much.

Signed-off-by: Richard Purdie <richard.purdie at linuxfoundation.org>

diff --git a/lib/bb/siggen.py b/lib/bb/siggen.py
index bc96fd3..bb8203d 100644
--- a/lib/bb/siggen.py
+++ b/lib/bb/siggen.py
@@ -238,7 +238,6 @@ class SignatureGeneratorBasic(SignatureGenerator):
             with os.fdopen(fd, "wb") as stream:
                 p = pickle.dump(data, stream, -1)
                 stream.flush()
-                os.fsync(fd)
             os.chmod(tmpfile, 0664)
             os.rename(tmpfile, sigfile)
         except (OSError, IOError) as err: