HEADSUP: New i386 interrupt and SMP code..

John Baldwin jhb at FreeBSD.org
Mon Nov 3 08:30:17 PST 2003

On 02-Nov-2003 Jeff Roberson wrote:
> On Thu, 30 Oct 2003, John Baldwin wrote:
>> Coming very soon to a CVS tree near you are some very large changes to
>> the i386 interrupt and SMP code.  New features include:
>> - Runtime selection of using the I/O APICs or the AT PICs to route
>>   interrupts.
>> - I/O APICs can be used in a UP kernel or on a UP system that
>>   supplies either an MP Table or ACPI APIC Table.
>> - An SMP kernel can run on a UP machine.  This means that SMP
>>   can now be enabled in GENERIC and the SMP kernel config can die.
> The lock prefix is extremely expensive on the P4 systems that I have
> measured.  It makes lock cmpxchg 150 cycles vs 12.  On athlon this is not
> such a big deal since it goes to 25 cycles from 12.  We should measure the
> impact of compiling in the lock prefix on UP P4 systems before making this
> the default.
> Otherwise, this all sounds good.

Note that one can always compile a custom kernel if one needs it for
a specific application, but that this will increase the amount of
out-of-box support for i386.  This has also been a requested feature
for quite a while now.


John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/

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