[src/trunk]: src/doc Mention the limitation of enabling both NET_MPSAFE and ALTQ

[ozaki-r <ozaki-r%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/5b8eb68fc233
branches:  trunk
changeset: 828248:5b8eb68fc233
user:      ozaki-r <ozaki-r%NetBSD.org@localhost>
date:      Tue Dec 05 03:23:29 2017 +0000

description:
Mention the limitation of enabling both NET_MPSAFE and ALTQ

diffstat:

 doc/TODO.smpnet |  11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diffs (22 lines):

diff -r bf9d7d2a08e7 -r 5b8eb68fc233 doc/TODO.smpnet
--- a/doc/TODO.smpnet   Tue Dec 05 02:57:37 2017 +0000
+++ b/doc/TODO.smpnet   Tue Dec 05 03:23:29 2017 +0000
@@ -1,4 +1,4 @@
-$NetBSD: TODO.smpnet,v 1.17 2017/11/20 09:01:20 ozaki-r Exp $
+$NetBSD: TODO.smpnet,v 1.18 2017/12/05 03:23:29 ozaki-r Exp $
 
 MP-safe components
 ==================
@@ -173,3 +173,12 @@
 already MP-safe, however, device drivers that use the data should also be fixed.
 A typical change should be to protect manipulations of the data via ETHER_*
 macros such as ETHER_FIRST_MULTI by ETHER_LOCK and ETHER_UNLOCK.
+
+ALTQ
+----
+
+If ALTQ is enabled in the kernel, it enforces to use just one Tx queue (if_snd)
+for packet transmissions, resulting in serializing all Tx packet processing on
+the queue.  We should probably design and implement an alternative queuing
+mechanism that deals with multi-core systems at the first place, not making the
+existing ALTQ MP-safe because it's just annoying.