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Re: Another comment on performance

From: Branko Čibej <brane_at_xbc.nu>
Date: Sat, 10 May 2008 03:04:33 +0200

Harvey, Edward wrote:
> 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.

That makes perfect sense. Double the number of threads and you'll (try
to) double the rate of seeks -- and seek time is a bottleneck.

> 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)

Yup -- with more disks, you get more spindles to distribute the seeks on
in parallel.

(But do note that "it all boils down to seeks" is way too naïve an

-- Brane

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Received on 2008-05-10 03:05:25 CEST

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