On 7/17/2012 12:26 AM, Dave Chinner wrote: ... > I bet it's single threaded, which means it is: The data given seems to strongly suggest a single thread. > Which means throughput is limited by IO latency, not bandwidth. > If it takes 10us to do the write(2), issue and process the IO > completion, and it takes 10us for the hardware to do the IO, you're > limited to 50,000 IOPS, or 200MB/s. Given that the best being seen > is around 35MB/s, you're looking at around 10,000 IOPS of 100us > round trip time. At 5MB/s, it's 1200 IOPS or around 800us round > trip. > > That's why you get different performance from the different raid > controllers - some process cache hits a lot faster than others. ... > IOWs, welcome to Understanding RAID Controller Caching Behaviours > 101 :) It would be somewhat interesting to see Stefan's latency and throughput numbers for 4/8/16 threads. Maybe the sysbench "--num-threads=" option is the ticket. The docs state this is for testing scheduler performance, and it's not clear whether this actually does threaded IO. If not, time for a new IO benchmark. -- Stan _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
