docs/153738: [patch] Docuement requirement to alter some sysctls when using igb(4) with jumbo frames.

[Tom Judge]

>Number:         153738
>Category:       docs
>Synopsis:       [patch] Docuement requirement to alter some sysctls when using igb(4) with jumbo frames.
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-doc
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Thu Jan 06 18:20:05 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Tom Judge
>Release:        FreeBSD 8.1-STABLE amd64
>Organization:
>Environment:
System: FreeBSD tinderbox.home.tomjudge.com 8.1-STABLE FreeBSD 8.1-STABLE #0 r213720: Tue Oct 12 14:02:02 UTC 2010 tj at tinderbox.home.tomjudge.com:/usr/obj/usr/src/sys/GENERIC amd64

>Description:

The attach patch (against current) documents the requirement to tune nmbcluster releated tuneables when using jumbo frames.

This tuning requirement is not obvious from error messages reported by the driver or the output of netstat -m.

Reviewed by: gjb@

Tom

>How-To-Repeat:
>Fix:

--- igb.4.txt begins here ---
Index: igb.4
===================================================================
--- igb.4	(revision 216409)
+++ igb.4	(working copy)
@@ -161,6 +161,18 @@
 If set to 1, enable Adaptive Interrupt Moderation.
 The default is to enable Adaptive Interrupt Moderation.
 .El
+.Pp
+If using jumbo frames with this driver, it is worth
+configuring the following sysctls, as the default settings
+for the card will require more resources than the default.
+.Bl -tag -width indent
+.It Va kern.ipc.nmbclusters
+The maximum number of mbuf clusters allowed.
+.It Va kern.ipc.nmbjumbo9k
+The maximum number of mbuf 9k jumbo clusters allowed.
+Increasing this to allow for at least 8192 extra clusters
+per interface should allow for an mtu of 8192.
+.El
 .Sh DIAGNOSTICS
 .Bl -diag
 .It "igb%d: Unable to allocate bus resource: memory"
--- igb.4.txt ends here ---


>Release-Note:
>Audit-Trail:
>Unformatted: