On Sat, Mar 14, 2009 at 9:39 AM, Vineet Agarwal <checkout.vineet@xxxxxxxxx> wrote: > On Fri, Mar 13, 2009 at 9:43 PM, Greg Freemyer <greg.freemyer@xxxxxxxxx> wrote: >> On Fri, Mar 13, 2009 at 11:58 AM, Manish Katiyar <mkatiyar@xxxxxxxxx> wrote: >>> On Fri, Mar 13, 2009 at 9:19 PM, Greg Freemyer <greg.freemyer@xxxxxxxxx> wrote: >>>> 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 >>>>> >>>> > Hello Greg , > >>>> 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. >>>> > > Thank you for your help . > well i had copied the file test_256.db after a fresh reboot. > Moreover, relocation of the file using memcopy algorithm was also performed > after a successful remount of file system. As i thought all pages > would have got synced > at the time of unmount. > >>>> I can't remember offhand how to flush the read cache >>> >>> By any chance it is setting 1 to /proc/sys/vm/drop_caches ?? >>> >> >> Looks right. Per http://linux-mm.org/Drop_Caches >> >> Your script should have: >> >> # flush the dirty blocks out to disk >> sync >> >> # flush the cache of all non-dirty blocks. ie. flush the read cache >> echo 3 > /proc/sys/vm/drop_caches >> >> # time the actual copy >> time (....; sync) >> > > well i have tried cp after following above steps > then the oputput is as follows > > [root@fscops Memcopy]# time cp /test_256.db /mnt > real 0m22.474s > user 0m0.016s > sys 0m1.501s > I still don't see a concluding sync. It is mandatory and it has to be within the parens. ie. time (cp /test_256.db /mnt; sync) 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
