RELENG_7 em problems (and RELENG_8)

[Jack Vogel]

The guy who worries about the Linux driver's performance is in my team, and
he's
a very good engineer, and we're talking about the hardware's DMA, so its not
an OS issue, thus I'm not saying I'm sure, but I'm dubious about this, at
least
when we're talking about igb. But hey, I'm willing to be proven wrong :)

Jack


On Tue, Aug 17, 2010 at 12:47 PM, Pyun YongHyeon <pyunyh at gmail.com> wrote:

> On Tue, Aug 17, 2010 at 12:34:31PM -0700, Jack Vogel wrote:
> > I believe the requirement of a context descriptor for most frames in the
> igb
> > driver
> > is just the way the hardware works, I've looked over the Linux driver
> again
> > and it
> > looks like they require the same. I don't believe its a big deal, just
> the
> > added
> > descriptor for the frame.
> >
>
> Setting up context does not cost much. The real cost comes from
> stopping requesting DMA for next packet whenever a new context
> is written.
> AFAIK Linux always added a new checksum context. I don't know
> whether Linux cares about the cost of refilling pipeline or
> measured the performance differences. FreeBSD noticed the
> difference on em(4) controllers and took appropriate action to take
> full advantage of the hardware feature, I think.
> I have to experiment how igb(4) works when it is told to reuse
> configured context(both checksum and TSO context).
>
>