Dickon Hood wrote: > On Fri, Dec 07, 2007 at 12:38:11 +0000, Darren J Moffat wrote: > : Dickon Hood wrote: > : >We've got an interesting application which involves recieving lots of > : >multicast groups, and writing the data to disc as a cache. We're > : >currently using ZFS for this cache, as we're potentially dealing with a > : >couple of TB at a time. > > : >The threads writing to the filesystem have real-time SCHED_FIFO priorities > : >set to 25. The processes recovering data from the cache and moving it > : >elsewhere are niced at +10. > > : >We're seeing the writes stall in favour of the reads. For normal > : >workloads I can understand the reasons, but I was under the impression > : >that real-time processes essentially trump all others, and I'm surprised > : >by this behaviour; I had a dozen or so RT-processes sat waiting for disc > : >for about 20s. > > : Are the files opened with O_DSYNC or does the application call fsync ? > > No. O_WRONLY|O_CREAT|O_LARGEFILE|O_APPEND. Would that help?
Don't know if it will help, but it will be different :-). I suspected that since you put the processes in the RT class you would also be doing synchronous writes. If you can test this it may be worth doing so for the sake of gathering another data point. -- Darren J Moffat _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
