On Tue, Apr 04, 2006 at 04:13:59PM +0100, Bahadir Balban wrote:
> Hi,
>
> I am trying to measure usb transfer throughput by timing file read
> operations from a usb flashdisk into main memory. The results seems to
> be imprecise and I suspect this is due to filesystem caching. How
> could I prohibit filesystem caching in the kernel?
I recently did the same thing. I used g_ether to do my benchmarking
and ttcp. You can use sync to help with the caching issue
like this:
#mount /dev/mmc /mnt
dd if=/dev/zero of=/mnt/4MB_file count=4096
#umount /dev/mmc
sync
I put that in a script
also you can use the open system call with O_SYNC
like this:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
char buf[4096*1024];
int main()
{
int fd, i;
fd = open("/mnt/sync_file", O_CREAT | O_SYNC | O_WRONLY);
//for(i=0;i<1000;i++) {
write(fd, buf, 4096*1024);
// }
}
from man page:
O_SYNC The file is opened for synchronous I/O. Any writes on the
resulting file descriptor will block the calling process until
the data has been physically written to the underlying hard-
ware. See RESTRICTIONS below, though.
you can also try using rawdevice
http://www.linux.com/howtos/SCSI-2.4-HOWTO/rawdev.shtml
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