SMP and setrunnable()- scheduler 4bsd

John Baldwin jhb at
Wed Jul 9 08:38:21 PDT 2003

On 09-Jul-2003 Terry Lambert wrote:
> John Baldwin wrote:
>> This is why HLT is not enabled in SMP by default (or at least was,
>> it may be turned on now).  Given that the clock interrupts are
>> effectively broadcast to all CPU's one way or another for all
>> arch's (that I know of), you will never halt more than the interval
>> between clock ticks on any CPU.
> I thought that there was either a SPARC or Alpha box where Poul
> had to mess with the divider because they were delivered round
> robin, instead?

No.  The only anomaly I know of is that on Alpha 2100's, the clock
interrupt seems to be round robin rather than broadcast (it is broadcast
on all other SMP Alpha's as far as we can tell.)  So far we aren't sure
exactly how off it is so there isn't a correction in the tree.


John Baldwin <jhb at>  <><
"Power Users Use the Power to Serve!"  -

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