> $ gcc -Wall -O -DINIT_WRITE tfsync.c
> $ time a.out
>
> real 1m15.11s
> user 0m0.04s
> sys 0m32.76s
>
> Note the large amount of system time here, and the fact that the extra
> time in INIT_WRITE is all system time. I have previously
> observed that fsync() on HPUX 10.20 appears to iterate through every
> kernel disk buffer belonging to the file, presumably checking their
> dirtybits one by one. The INIT_WRITE form loses because each fsync in
> the second loop has to iterate through a full 16Mb worth of buffers,
> whereas without INIT_WRITE there will only be as many buffers as the
> amount of file we've filled so far. (On this platform, it'd probably
> be a win to use log segments smaller than 16Mb...) It's interesting
> that there's no visible I/O cost here for the extra write pass ---
> the extra I/O must be completely overlapped with the extra system time.
Tom, could you run this test for different block sizes?
Up to 32*8k?
Just curious when you get something close to
> $ gcc -Wall -O -DINIT_WRITE -DUSE_ODSYNC tfsync.c
> $ time a.out
>
> real 0m21.40s
> user 0m0.02s
> sys 0m0.60s
Vadim