> Date: Thu, 25 Nov 2010 12:30:39 +0000
quoted text
> From: Owain Ainsworth <zerooa@googlemail.com>
> 
> On Thu, Nov 25, 2010 at 11:50:06AM +0100, Claudio Jeker wrote:
> > On Wed, Nov 24, 2010 at 05:42:59PM +0100, Mike Belopuhov wrote:
> > > On Wed, Nov 24, 2010 at 17:06 +0100, Claudio Jeker wrote:
> > > > This diff was made by oga@ some time ago -- I just fixed a few conflicts
> > > > and I would really like to see this going in.
> > > > 
> > > > netisr needs to be made a normal C function and not this madness it
> > > > currently is. This is necessary to imporve the packet scheduling.
> > > > 
> > > > Tested myself on i386, amd64, sparc64, sparc, alpha and hppa
> > > 
> > > hi,
> > > 
> > > i like the diff, but why not get rid of netisr_dispatch.h?
> > 
> > I planned to this after this diff goes in. I did not want to change
> > Owain's initial diff too much so I left that out for now.
> 
> Miod pointed out to me when I first sent this out that some archs use
> something slightly different than this generic version.
> 
> For example hppa uses a specially aligned netisr variable so it can use
> the pa-risc real atomic instructions which are quite a bit faster.

Especially on MP kernels.

quoted text
> Similarly x86 uses compare-and-swap instead of test, then clear bits.
> 
> I meant to add some MD defines so that this could be kept (falling back
> to the implementation in this diff)  since miod claims that it is useful
> and significantly faster (I did not check this). I've cced miod so he
> can answer with somewhat more authority.

The hppa and i386/amd64 approach are rather similar.  Both do an
atomic load and clear, which happens to be the only atomic instruction
available on hppa, and is easy to implement as an atomic swap with 0
on i386/amd64.  But implementing this operation on other architectures
shouldn't be much more difficult, and should work just as well as the
proposed code that uses atomic_clearbits_int().  The MI code would
look something like:

void
netintr(void *unused)
{
	int n;

	n = atomic_load_and_clear(&netisr);
#define DONETISR(bit, fn)			\
		do {				\
			if (n & 1 << (bit))	\
				fn();		\
		} while ( /* CONSTCOND */ 0)
#include <net/netisr_dispatch.h>
}