svn commit: r357051 - head/sys/dev/bge

[Gleb Smirnoff]

On Thu, Jan 23, 2020 at 08:33:58PM -0500, Ryan Stone wrote:
R> > Because at interrupt level we can batch multiple packets in a single epoch.
R> > This speeds up unfiltered packet forwarding performance by 5%.
R> >
R> > With driver level pfil hooks I would claim even more improvement, because before
R> > the change we needed to enter epoch twice - once for filtering, than for ether_input.
R> >
R> > Epoch isn't a layer, it is a synchronisation primitive, so I disagree about
R> > statement on layering violation.
R> 
R> Epoch is a synchronization primitive, but the net_epoch is absolutely
R> a part of the networking layer.  If we need better batching then the
R> correct solution is to introduce a batched interface for drivers to
R> push packets up the stack, not to mess around at the interrupt layer.

Such interface of course would be valuable but will not cover case
when an interrupt arrives during processing of previous one. So its
batching possiblities are limited compared to interrupt level batching.

And I already noted that ether_input() isn't the only way to enter
the network stack.

R> Note that the only reason why this works for mlx4/mlx5 is that
R> linuxkpi *always* requests a INTR_TYPE_NET no matter what driver is
R> running.  This means that all drm graphics driver interrupts are now
R> running under the net_epoch:
R> 
R> https://svnweb.freebsd.org/base/head/sys/compat/linuxkpi/common/include/linux/interrupt.h?revision=352205&view=markup#l103

Well, it is not my fault that a video driver requests INTR_TYPE_NET
interrupt. I mean, you can't put this as a rationale against using
network epoch for all interrrupts that declare theirselves as network
interrupts. However, this is harmless.

-- 
Gleb Smirnoff