Messages in this thread | | | Subject | io priorities? | Date | Thu, 01 Jul 2004 12:14:05 -0600 | From | Sebastian Kuzminsky <> |
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Hi folks, i've got IO problems...
I've got a computer with one IDE disk. There are a couple of processes writing big telemetry logs, totally not time-critical. Then there's one process periodically writing a tiny little state file, about 150 bytes. The process with the state file wants to sync its file to disk and then quickly be back and running. When it calls fsync() it has to wait for other processes' less-important pending I/O before it gets to complete, and it's not unusual for this to take 30 seconds (CF over IDE), which is too slow for my application.
This happens with both 2.4.23 and 2.6.6 (as, cfq, & deadline). I havent tried to tune the schedulers at all, just using the default values.
I've tried five methods of syncing the file: sync(), fsync(), fdatasync(), and opening with O_SYNC or O_DSYNC. All take about the same amount of time.
I've tried it on my target machine (Compact Flash via pio IDE) and on my development machine (regular hard drive via udma5 IDE). Same results qualitatively speaking.
I read Jens Axboe's thread about cfq + io priorities, and it sounds perfect! I could give my one time-critical process high io priority and it should preempt the others and life would be fine. But all the l-k traffic i've found about this is from back in November. Did this work go anywhere?
Any suggestions on fixes or workarounds?
I'm stumped.
-- Sebastian
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