Device Polling code for -current.

Non-SMP, i386-only, no polling in the idle loop at the moment.

To use this code you must compile a kernel with

        options DEVICE_POLLING

and at runtime enable polling with

        sysctl kern.polling.enable=1

The percentage of CPU reserved to userland can be set with

        sysctl kern.polling.user_frac=NN (default is 50)

while the remainder is used by polling device drivers and netisr's.
These are the only two variables that you should need to touch. There
are a few more parameters in kern.polling but the default values
are adequate for all purposes. See the code in kern_poll.c for
more details on them.

Polling in the idle loop will be implemented shortly by introducing
a kernel thread which does the job. Until then, the amount of CPU
dedicated to polling will never exceed (100-user_frac).
The equivalent (actually, better) code for -stable is at

	http://info.iet.unipi.it/~luigi/polling/

and also supports polling in the idle loop.

NOTE to Alpha developers:
There is really nothing in this code that is i386-specific.
If you move the 2 lines supporting the new option from
sys/conf/{files,options}.i386 to sys/conf/{files,options} I am
pretty sure that this should work on the Alpha as well, just that
I do not have a suitable test box to try it. If someone feels like
trying it, I would appreciate it.

NOTE to other developers:
sure some things could be done better, and as always I am open to
constructive criticism, which a few of you have already given and
I greatly appreciated.
However, before proposing radical architectural changes, please
take some time to possibly try out this code, or at the very least
read the comments in kern_poll.c, especially re. the reason why I
am using a soft netisr and cannot (I believe) replace it with a
simple timeout.

Quick description of files touched by this commit:

sys/conf/files.i386
        new file kern/kern_poll.c
sys/conf/options.i386
        new option
sys/i386/i386/trap.c
        poll in trap (disabled by default)
sys/kern/kern_clock.c
        initialization and hardclock hooks.
sys/kern/kern_intr.c
        minor swi_net changes
sys/kern/kern_poll.c
        the bulk of the code.
sys/net/if.h
        new flag
sys/net/if_var.h
        declaration for functions used in device drivers.
sys/net/netisr.h
        NETISR_POLL
sys/dev/fxp/if_fxp.c
sys/dev/fxp/if_fxpvar.h
sys/pci/if_dc.c
sys/pci/if_dcreg.h
sys/pci/if_sis.c
sys/pci/if_sisreg.h
        device driver modifications

1 files changed, 14 insertions, 0 deletions

diff --git a/sys/kern/kern_intr.c b/sys/kern/kern_intr.c
index e873c6e..88868dc 100644
--- a/sys/kern/kern_intr.c
+++ b/sys/kern/kern_intr.c
@@ -623,7 +623,16 @@ swi_net(void *dummy)
 	u_int bits;
 	int i;
 
+#ifdef DEVICE_POLLING
+    for (;;) {
+	int pollmore;
+#endif
 	bits = atomic_readandclear_int(&netisr);
+#ifdef DEVICE_POLLING
+	if (bits == 0)
+		return;
+	pollmore = bits & (1 << NETISR_POLL);
+#endif
 	while ((i = ffs(bits)) != 0) {
 		i--;
 		if (netisrs[i] != NULL)
@@ -632,6 +641,11 @@ swi_net(void *dummy)
 			printf("swi_net: unregistered isr number: %d.\n", i);
 		bits &= ~(1 << i);
 	}
+#ifdef DEVICE_POLLING
+	if (pollmore)
+		ether_pollmore();
+    }
+#endif
 }
 
 /*