Hello Yongjian Zhang, On Thu, 2010-01-07 at 18:29 -0700, Brent Yardley wrote: > > Here are a couple of thoughts. > > Disktest will force a sync at the end of all write IO operations, when > not raw / directio, this sync can take quite a bit of time depending > on how full the buffer cache is. This additional time to sync the IO > to the disk is added to the overall IO time, it assumes that > performance is to measure the time it takes to get the data to the > disk, and this may be what is causing the difference between what you > are seeing between dd and disktest. Also, dd will perform a > sequential copy, the default for disktest is to perform random seeks, > so you will need to add a -pl to the command line to compare disktest > with dd. > > I have been working on an experimental patch to time IOs in disktest > at the usec level and to only include the time when IO was actually in > flight, ie. from the start to end of each write/read command this will > also exclude an time it takes to sync to the disk. This is more > in-line I believe with how dd measures the throughput. I have > included the patch here if you would like to try it out, and see if > the numbers more closely match what you are seeing in dd. > > > > If you want to specifically understand the performance of the device > your testing, I would recommend using the -Ibd option. This will > force the bypass of kernel buffer caching and will be testing the > performance of the device and transport only. > > Another test that is useful and tests the specific performance of the > transport for devices that have caching enabled, is to use the -S0:0 > option with the -Ibd options. This forces disktest to always request > the block data from the same block. When used with a high -B and -K, > this should give you your max throughput, and used with a small -B and > high -K, this will give you your make IOPS. > > Let me know how things go or if you have further questions.
Did you get an opportunity to test this patch ? Kindly let us know, i would then check this in. Regards-- Subrata > Thanks, > Brent > > > > From: > Subrata Modak > <[email protected]> > To: > Yongjian Zhang > <[email protected]> > Cc: > [email protected], > Brent Yardley/Beaverton/i...@ibmus > Date: > 01/07/2010 03:06 AM > Subject: > Re: [LTP] disktest question > > > ______________________________________________________________________ > > > > > On Tue, 2010-01-05 at 10:23 -0700, Yongjian Zhang wrote: > > Hi all, > > > > I'm trying to use disktest to measure the performance of an iSCSI > device but > > get extremely low throughput... > > > > How about the following manpage inside LTP source: > > # man ./testcases/kernel/io/disktest/man1/disktest.1 > > Regards-- > Subrata > > > For example, I did > > > > disktest -w -S0:1k -B 1024 /dev/sdb (/dev/sdb is the iSCSI device > file, no > > partition or file system on it) > > > > And the result was: > > | 2010/01/05-02:58:26 | START | 27293 | v1.4.2 | /dev/sdb | Start > > args: -w -S0:1024k -B 1024 -PA (-I b) (-N 8385867) (-K 4) (-c) (-p > R) > > (-L 1048577) (-D 0:100) (-t 0:2m) (-o 0) > > | 2010/01/05-02:58:26 | INFO | 27293 | v1.4.2 | /dev/sdb | Starting > > pass > > ^C| 2010/01/05-03:00:58 | STAT | 27293 | v1.4.2 | /dev/sdb | Total > > bytes written in 85578 transfers: 87631872 > > | 2010/01/05-03:00:58 | STAT | 27293 | v1.4.2 | /dev/sdb | Total > > write throughput: 701055.0B/s (0.67MB/s), IOPS 684.6/s. > > | 2010/01/05-03:00:58 | STAT | 27293 | v1.4.2 | /dev/sdb | Total > > Write Time: 125 seconds (0d0h2m5s) > > | 2010/01/05-03:00:58 | STAT | 27293 | v1.4.2 | /dev/sdb | Total > > overall runtime: 152 seconds (0d0h2m32s) > > | 2010/01/05-03:00:58 | END | 27293 | v1.4.2 | /dev/sdb | User > > Interrupt: Test Done (Passed) > > > > As you can see, the throughput was only 0.67MB/s and only 85578 > > written in 87631872 transfers... > > I also tweaked the options with "-p l" and/or "-I bd" (change seek > > pattern to linear and/or speficy IO type as block and direct IO) but > > no improvement happened... > > > > I thought this low throughput could be caused by the link rate or > disk > > problem, but dd ruled it out.. > > > > $ dd if=/dev/zero of=/dev/sdb bs=1024 count=1048576 > > > > The throughput is 7.2 MB/s. > > > > There must be something I've done wrong with disktest... Could > anyone maybe > > help me out here? > > > > Thanks a lot! > > > > jack > > > > > > > ------------------------------------------------------------------------------ > > This SF.Net email is sponsored by the Verizon Developer Community > > Take advantage of Verizon's best-in-class app development support > > A streamlined, 14 day to market process makes app distribution fast > and easy > > Join now and get one step closer to millions of Verizon customers > > http://p.sf.net/sfu/verizon-dev2dev > > _______________________________________________ > > Ltp-list mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/ltp-list > > > ------------------------------------------------------------------------------ This SF.Net email is sponsored by the Verizon Developer Community Take advantage of Verizon's best-in-class app development support A streamlined, 14 day to market process makes app distribution fast and easy Join now and get one step closer to millions of Verizon customers http://p.sf.net/sfu/verizon-dev2dev _______________________________________________ Ltp-list mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/ltp-list
