There is a limitiation on the number of interrupt vectors available when only a single processor is running. To have more interrupts available we need to start SMP earlier when building a monotolith kernel and not loading drivers as modules. The driver in question is a network driver and because it cannot be started after SI_SUB_ROOT_CONF due to PXE support I see no other option than to move SI_SUB_SMP earlier.

Suggested patch:

Index: sys/kernel.h
--- sys/kernel.h        (revision 276691)
+++ sys/kernel.h        (working copy)
@@ -152,6 +152,7 @@
        SI_SUB_KPROF            = 0x9000000,    /* kernel profiling*/
        SI_SUB_KICK_SCHEDULER   = 0xa000000,    /* start the timeout events*/
        SI_SUB_INT_CONFIG_HOOKS = 0xa800000,    /* Interrupts enabled config */
+       SI_SUB_SMP              = 0xa850000,    /* start the APs*/
        SI_SUB_ROOT_CONF        = 0xb000000,    /* Find root devices */
        SI_SUB_DUMP_CONF        = 0xb200000,    /* Find dump devices */
        SI_SUB_RAID             = 0xb380000,    /* Configure GEOM classes */
@@ -165,7 +166,6 @@
        SI_SUB_KTHREAD_BUF      = 0xea00000,    /* buffer daemon*/
        SI_SUB_KTHREAD_UPDATE   = 0xec00000,    /* update daemon*/
        SI_SUB_KTHREAD_IDLE     = 0xee00000,    /* idle procs*/
-       SI_SUB_SMP              = 0xf000000,    /* start the APs*/
        SI_SUB_RACCTD           = 0xf100000,    /* start racctd*/
        SI_SUB_LAST             = 0xfffffff     /* final initialization */

This fixes a problem for Mellanox drivers in the OFED layer. Possibly we need to move the SMP even earlier to not miss the generic FreeBSD PCI device enumeration or maybe this is not possible. Does anyone know how early we can start SMP?

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