kern/170713: [cxgb] Driver must be loaded after boot due to timing issues checking for kern.ipc.nmb* values set via /boot/loader.conf

[Navdeep Parhar]

The following reply was made to PR kern/170713; it has been noted by GNATS.

From: Navdeep Parhar <np at FreeBSD.org>
To: bug-followup at FreeBSD.org, yanegomi at gmail.com
Cc:  
Subject: Re: kern/170713: [cxgb] Driver must be loaded after boot due to timing
 issues checking for kern.ipc.nmb* values set via /boot/loader.conf
Date: Wed, 22 Aug 2012 17:56:34 -0700

 First, note that only kern.ipc.nmbclusters is a valid tunable.  The rest 
 of the nmbXXX settings in your loader.conf have no effect.  There are 
 sysctls but no tunables for the rest.
 
 Take a look at tunable_mbinit in kern_mbuf.c -- on recent FreeBSD 
 versions it starts with nmbclusters and sizes others based on this.  You 
 can set nmbclusters really high and influence the values of the other 
 parameters.
 
 In my opinion we should have a TUNABLE_INT_FETCH for all of the nmbXXX 
 and autocalculate the ones that are not set, just like what we do for 
 nmbclusters today.
 
 static void
 tunable_mbinit(void *dummy)
 {
 	TUNABLE_INT_FETCH("kern.ipc.nmbclusters", &nmbclusters);
 
 	/* This has to be done before VM init. */
 	if (nmbclusters == 0)
 		nmbclusters = 1024 + maxusers * 64;
 	nmbjumbop = nmbclusters / 2;
 	nmbjumbo9 = nmbjumbop / 2;
 	nmbjumbo16 = nmbjumbo9 / 2;
 }
 
 
 Compare this to the tunable_mbinit in 7 and you can see why the 
 nmbclusters tunable does not affect the others -- it is updated after 
 the other values have already been calculated.
 static void
 tunable_mbinit(void *dummy)
 {
 
 	/* This has to be done before VM init. */
 	nmbclusters = 1024 + maxusers * 64;
 	nmbjumbop = nmbclusters / 2;
 	nmbjumbo9 = nmbjumbop / 2;
 	nmbjumbo16 = nmbjumbo9 / 2;
 	TUNABLE_INT_FETCH("kern.ipc.nmbclusters", &nmbclusters);
 }
 
 Regards,
 Navdeep