On Fri, Mar 13, 2009 at 11:23 AM, Vineet Agarwal <checkout.vineet@xxxxxxxxx> wrote: > Hello Everyone, > > Well i have tested the code of memcopy without sync_dirty_buffers() > No data corruption was reported. So it is fine . > But still the downtime for relocation is still high as compared to cp. > > test_256.db is a 256 Mb file that is relocated. > > [root@fscops Memcopy]# time cp /test_256.db /mnt > real 0m17.577s > user 0m0.017s > sys 0m1.251s > Vineet, You have to remember all the caches that are involved with disk i/o. When benchmarking you have to ensure all the caches are empty before AND after the timing is performed. ie. Having a copy of test_256.db in the cache before you start would mean it does not have to be read from disk, but simply pulled from ram. Not emptying the cache at the end means all that your timing is the population of the write cache. Need to include the time it takes to get the data to disk. I can't remember offhand how to flush the read cache, but you can flush the write cache by calling sync. So I would modify your cp benchmark to at least do: sync; time (cp /tmp/test_256.db /tmp/junk; sync) But as I say the read cache is likely to have a copy of test_256.db already in it, so you can't trust even the above. What I typically do is to use a test file several times the size of my RAM, then run a test like the above several times in a row. Because the test file is much bigger than you cache, it is a pretty safe _assumption_ that you don't have any useful data in the cache to accelerate the read. Once you get a more accurate cp benchmark, then please redo the kernel module test as: sync time (insmod mmcpy.ko inum=12; sync) It is important to note that the above are very basic benchmarking techniques. To properly benchmark you need to control the details of the cache much more so, but for the purposes of comparing these 2 methods I think the above should be fine. Good luck, Greg -- Greg Freemyer Head of EDD Tape Extraction and Processing team Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
