Dnia 2010-05-07, pią o godzinie 09:47 -0400, Patrik Lahti pisze:
> On 07/05/10 05:57 AM, Tomasz Lis wrote:
> > Thank you, Patrik.
> >
> > Based on your answer, I was able to create the native TAP driver which supports cloning.
> >
> > There are still some issues with stability, but it works.
> >
> > The major problem is that when I'm using it to just redirect packets, it takes ~90ms before I got an answer I've 
sent to myself. Under linux, the same task takes ~0.080 ms.
> >
> > I made a time logging in the driver, and I can see that delay between if_input() call to send a packet, and 
if_start() call which informs that there's a return, if ~60ms; rest of the delay is probably made by my logging routines
.
> >
> > Is there any way to make the io-pkt stack work faster?
> >    
> Io-pkt is faster.
> 
> Sounds like something isn't right somewhere. What driver is being used 
> (i.e. is calling ifp->if_input())? Is bridging, fast IP forwarding, or 
> regular IP forwarding taking place between the device and the tap 
> interface? You can capture and analyze a kernel event trace to see what 
> thread is doing and why...
> 
> /P

It seems that the delay is generated when sending packets (using write()
to put packets on network stack). I verified that using the TAP made by
Oleg Bolshakov - his TAP sends packets in less than 1 ms. When I used
his driver to write() and my driver read(), times were still under 1ms.

Interesting thing is that when I'm sending next packet, the previous one
is delivered without delay - for example when using:
ping -i 0.01 <TAP_ADDRESS>
I'm getting time=9ms, while for:
ping -i 0.04 <TAP_ADDRESS>
I'm getting time=39ms.
If the interval is over 0.1, delivery time stays at ~100 ms.


I'm calling if_input() from a resource manager thread, like this:

----
	pthread_mutex_lock(&sc->sc_mutex);
	ifp->if_ipackets++;
	// ip_input() needs this
	m->m_pkthdr.rcvif = ifp;

	LOG("%s: calling if_input()", sc->sc_dev.dv_xname);
#if NBPFILTER > 0
	if (ifp->if_bpf)
		bpf_mtap(ifp->if_bpf, m);
#endif
	s =splnet();
	(*ifp->if_input)(ifp, m);
	splx(s);
	pthread_mutex_unlock(&sc->sc_mutex);
	_IO_SET_WRITE_NBYTES(ctp, msg->i.nbytes);
	LOG("%s: packet %d sent", sc->sc_dev.dv_xname, (int)ifp->if_ipackets);
	(*ifp->if_input)(ifp, NULL);
	return (_RESMGR_NPARTS(0));
----

Both LOG messages: "tap0: calling if_input()" and "tap0: packet <x>
sent" are written to log at same time, but I have to wait 100ms before
tap_start() is called.

I'm forwarding packets in a test program, in short:
----
    fd = open("/dev/tap0", O_RDWR);
    for (n=0;;n++)
    {
        len = read(fd, buff, sizeof(buff) );
        if (len < 0)
            break;
        eh = (eth *)buff;
        if (eh->etype == 0x0008)
        {
            iph = (ip *)&eh->data1;
            // switch IPs
            for (i=0;i<4;i++)
            {
                addr[i] = iph->ip_src[i];
                iph->ip_src[i] = iph->ip_dst[i];
                iph->ip_dst[i] = addr[i];
            }
            write(fd, buff, len);
        }
    }
----