Another comment on performance
From: Harvey, Edward <Edward.Harvey_at_patni.com>
Date: Fri, 9 May 2008 16:23:38 -0400
I have been benchmarking many different systems and platforms over the last week or two. My findings, I think, probably won't have much effect here, given the present direction of WC rewrite, but I figure it's at least worth mention.
The benchmark is: (Before beginning) Create a large directory of small files. Reboot to completely clear any caching. And then time how long it takes to scan through those files. Repeat with varying numbers of threads, on varying hardware types, rebooting each time to invalidate cache.
Let's take a typical PC as the measuring stick. One sata disk, plenty of memory & core2 duo processor. I'll call the speed of this machine 1.0x. (1m 04s to scan 100,000 files)
I found that if scanning a large directory tree on the one-disk pc, if you use multiple threads, it hurts performance. Test was repeated with 2 threads, 5 threads, and 10 threads. Each test successively worse than the previous. 1m22s , 1m34s , 1m38s. Each sample was taken 3 times, and never varied more than 1s.
I ran the same tests on a typical RAID5 server - 8 sata 7200rpm disks, raid5 + hotspare = capacity & speed of 6 disks, with caching raid controller card.
I found with 1 thread, the server performance scanning a large directory of files is about 1.4x (0m 44s to scan 100,000 files)
I found with 5-10 threads, the server performance is about 2x. (10 threads, 0m 32s to scan 100,000 files)
The point was simply to see how threading helps or hinders performance, by trying to fully leverage the hardware available.
Single Disk, 1 thread 1.0x (3 samples)
RAID5 Disks, 1 thread 1.45x (2 samples)
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