Update pbr: remove sync slowdown ?

[bigsmile74]

What's the reason to use sync? Most of it runs in-memory or on a tmpfs. If you let Linux handle it will save about ~5 seconds in a restart.

I only see it used in the following init files with a good reason:

• boot: to cement initial config generation.
• done: after removal of sysupgrade (substantial file size)
• uhttpd to cement the certificate
• umount to cement pending writes

I experience no issues by removing them.

before:

# time /etc/init.d/pbr restart
real	0m 7.62s
user	0m 1.31s
sys	0m 0.37s

after:

# time ./pbr restart
real	0m 2.37s
user	0m 1.33s
sys	0m 0.40s

[bigsmile74]

Also and I did not mention this, there is the penalty of wear-leveling if users run from NAND/NOR flash. So by letting those writes accumulate in cache it would only write the end result. If you still want a sync, I would do it before the script exits and in the background eg: sync & then exit.

[stangri]

I believe when I first implemented the rt_tables updates there were issues with people ending up with corrupted tables, that's why the sync was implemented. The issue is if I accept the PR and start releasing new binaries, it may be a while until we get a corruption report. Again, let me sleep on this.