Re: RFC: gif(4) MP-ify

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Fri, 25 Dec 2015 17:49:35 +0900
   From: Kengo NAKAHARA <k-nakahara%iij.ad.jp@localhost>

   I MP-ify gif(4) interface and ip_encap which is required by gif(4).

   Here is the patch
       http://www.netbsd.org/~knakahara/gif-mp-ify/gif-mp-ify.patch

   Could you comment this patch?

I see a lot of rwlocks.  Can you describe the access patterns you
expect for these -- what operations require reader or writer locks,
how often are these operations done, and what contention you expect?

For large and complex operations, it may be worthwhile to allow
multiple readers by using an rwlock.  But reader locks still have high
contention to acquire and release.  So if we want an MP-scalable, not
merely MP-safe, network stack, I wonder whether it might be better to
use pserialize(9) instead of rwlock in some cases here -- or a
pserialize(9)-based rwlock, like fstrans.


P.S.  Thanks for all your work on MPifying the network stack -- it is
a big and scary job!