misc/93887: cpu_spinwait calls missing

[Arthur Hartwig]

>Number:         93887
>Category:       misc
>Synopsis:       cpu_spinwait calls missing
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Feb 27 06:50:04 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator:     Arthur Hartwig
>Release:        6.1-BETA1
>Organization:
Nokia
>Environment:
oz-net-11# uname -a
FreeBSD oz-net-11.nes.nokia.com 6.1-BETA1 FreeBSD 6.1-BETA1 #4: Tue Feb 21 14:01:31 EST 2006     root at oz-net-11.nes.nokia.com:/usr/src/sys/amd64/compile/oz-net-11  amd64


>Description:
There are five busy wait loops in kern/subr_smp.c which would be more "multi-processor friendly" on i386 and amd64 architectures if they included a call to cpu_spinwait(). On these architectures the cpu_spinwait() executes a pause instruction which the Intel IA32 architecture manual says "improves the performance of spin wait loops."

Loops which could include the call to cpu_spinwait() occur in stop_cpus(), stop_cpus_nmi(), restart_cpus(), and two in smp_rendezvous_action()
>How-To-Repeat:

>Fix:

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