On Wednesday 12 July 2006 2:54 am, Gyorgy Szekely wrote: > These numbers tell me that there's a huge overhead (at least 8ms) when > starting a transaction. Is this normal?
There's a per-transaction overhead, sure ... I'd expect max 2 msec (and more typically about 1 msec) comes from the host controller (which is "OHCI" not "OCHI"). Other delays can come from usb-storage and scsi ... there are multiple tasks involved. > The other problem is that the kernel is busy while waiting, if I set > the blocksize to 512 in my application the computing performance of > the system decreases dramatically. Then don't use 512 bytes!! You're basically doing block-at-a-time I/O, where each block involves multiple task switches. Likely it's the task switching that chews the most CPU overhead. There's a reason that block I/O systems avoid small blocks. They've been tuned for large blocks. Now it may be that the small-block speed here is lower than it should be, but you should never be surprised to see that small-block transfers go slowly. - Dave ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
