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Re: NetBSD 5.1 TCP performance issue (lots of ACK)

On Wed, Nov 02, 2011 at 08:04:40PM +0100, Manuel Bouyer wrote:
> On Sat, Oct 29, 2011 at 10:14:18PM +0200, Martin Husemann wrote:
> > On Sat, Oct 29, 2011 at 10:02:10PM +0200, Manuel Bouyer wrote:
> > > OK, I see. But, is there a platoform where BUS_DMASYNC_PREREAD is not
> > > a NOP ? I can't what kind of work BUS_DMASYNC_PREREAD could have to do ...
> > 
> > On platforms with memory reordering it might be a barrier (i.e. sparc64 does
> > a membar_sync() for it).
> So does x86. But I think it's redundant with the POSTREAD (which is also
> a barrier) we'll do later.

It looks to me, too, like the x86 implementation will make a redundant
x86_lfence() call.

I think it is preferable for the bus_dma implementation to try to avoid
redundant operations than for MI drivers to try to do so.  What do you


David Young             OJC Technologies is now Pixo     Urbana, IL   (217) 344-0444 x24

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