RE: iSCSI read/write cost difference

["Tony Battersby" <tonyb@cybernetics.com>]

> > I think the UNH iSCSI implementation dosen't set TCP_NODELAY on the
> > connection sockets, which can lead to strange performance 
> characteristics
> > like this.  See the man pages for "setsockopt" and "tcp".  
> You can find an
> > example of setting TCP_NODELAY in the linux-iscsi drivers at
> > http://sourceforge.net/projects/linux-iscsi.  Just download 
> the source and
> > grep for TCP_NODELAY.
> yes, it doesn't set the TCP_NODELAY. I read the linux-iscsi 
> code and try to 
> add this sock->ops->setsockopt() in UNH code. But it always 
> return EFAULT 
> indicating a bad address. but i use a similar way to define 
> arg = 1 as a 
> local variable. i am not sure why i am wrong. and i check the 
> inet_set_sockopt and tcp_setsock_opt, nowhere return a EFAULT.
> 
> can some one figure it out? thx.

For calling setsockopt() from kernel code, try something like this:

#include <asm/uaccess.h>

int arg = 1;
mm_segment_t oldfs;

oldfs = get_fs();
set_fs(get_ds());

if (sock->ops->setsockopt(sock,
                          IPPROTO_TCP,
                          TCP_NODELAY,
                          (char *) &arg,
                          sizeof(arg)) < 0)
   {
   /* handle error */
   }

set_fs(oldfs);

Anthony J. Battersby
Cybernetics