On Sun, Oct 10, 2010 at 2:08 PM, loody <miloody@xxxxxxxxx> wrote: > Dear all: > I am so SORRY that I send the mail before I finish it, since I finger > flip over the send button. > SORRY~~~ > > i write a simple program as below to count the speed of writing a file > over usb, gettimeofday before writing and gettimeofday when finish > writing. but I found something make me curious. > > 1. my program is compiled as static and I use open, write instead of > libc function calls. > > 2. I use the same kernel and usb modules, kernel version is 2.6.31 > the only difference is I have 2 rootfs, both of them are > cross-compiled as arm platform. > Here comes the problem. > the speed of the roofs1 I got is 8MB/s but rootfs2 is 1MB/s > > my concerns are: > 1. my program is build as static, that means the libs in the roofs has > nothing to do with this program. > 2. my program is written with file I/O, instead of file operations > supported by c lib, that means I direct calling kernel system call for > writing data. If my assumption above are correct, that seems the > kernel make me slow on rootfs2. > > 3. in the beginning, I thought there maybe some other program, like > threads, running on rootfs2 which let my speed get slow. > but how could I find them on the taret? > 4. if I really want to find out whether the delay comes from kernel > instead of usb or other driver module, is there configs I can open to > monitor the write flow and found out where it stuck? > appreciate your help, > miloody You don't describe how your flushing the cache. i find most out of whack benchmarks like this are caused by not properly managing the cache flushing process. Since you wrote your own "benchmark" tool, just be sure it calls fsync() before closing the file and taking your time measurement. Greg -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
