[CentOS] Strange messages after installing Quad-core processor

After installing a Phenom II X4 processor (replacing a single core Semperon) I 
am getting these messages on the console and in dmesg:

Warning Timer ISR/2: Time went backwards: delta=-250135996 delta_cpu=13864004 shadow=1355887856733 off=870052783 processed=1357008044419 cpu_processed=1356744044419
 0: 1357004044419
 1: 1356696044419
 2: 1356744044419
 3: 1356696044419
printk: 41 messages suppressed.
Warning Timer ISR/1: Time went backwards: delta=-59982686 delta_cpu=4017314 shadow=1360903191494 off=777060324 processed=1361740044419 cpu_processed=1361676044419
 0: 1361740044419
 1: 1361676044419
 2: 1361676044419
 3: 1361656044419
printk: 44 messages suppressed.
Warning Timer ISR/1: Time went backwards: delta=-1411977595 delta_cpu=480022405 shadow=1365903272832 off=72983745 processed=1367388044419 cpu_processed=1365496044419
 0: 1367384044419
 1: 1365496044419
 2: 1365552044419
 3: 1365552044419
printk: 46 messages suppressed.
Warning Timer ISR/3: Time went backwards: delta=-131987583 delta_cpu=56012417 shadow=1370651436789 off=820810871 processed=1371604044419 cpu_processed=1371416044419
 0: 1371600044419
 1: 1371444044419
 2: 1371444044419
 3: 1371416044419
printk: 31 messages suppressed.
Warning Timer ISR/2: Time went backwards: delta=-27979896 delta_cpu=20020104 shadow=1375888162629 off=588093398 processed=1376504044419 cpu_processed=1376456044419
 0: 1376504044419
 1: 1376460044419
 2: 1376456044419
 3: 1376456044419
printk: 47 messages suppressed.
Warning Timer ISR/1: Time went backwards: delta=-207976755 delta_cpu=60023245 shadow=1380903513990 off=672744302 processed=1381784044419 cpu_processed=1381516044419
 0: 1381784044419
 1: 1381516044419
 2: 1381516044419
 3: 1381500044419
printk: 49 messages suppressed.
Warning Timer ISR/2: Time went backwards: delta=-628613448 delta_cpu=135386552 shadow=1384888283123 off=959350632 processed=1386476044419 cpu_processed=1385712044419
 0: 1386476044419
 1: 1385624044419
 2: 1385712044419
 3: 1385712044419
printk: 60 messages suppressed.
Warning Timer ISR/2: Time went backwards: delta=-559977270 delta_cpu=240022730 shadow=1390888386502 off=47871477 processed=1391496044419 cpu_processed=1390696044419
 0: 1391496044419
 1: 1390820044419
 2: 1390696044419
 3: 1390696044419

The machine *appears* to be running fine.  Are these messages something I need 
to worry about?  I am running Xen and kernel 2.6.18-348.3.1.el5xen on the DOM0 
(host) VM under CentOS 5.9.

I just popped in the new processor -- should I have changed a BIOS setting or 
something? 

Boot params:

title CentOS (2.6.18-348.3.1.el5xen)
        root (hd0,0)
        kernel /xen.gz-2.6.18-348.3.1.el5 dom0_mem=3072M
        module /vmlinuz-2.6.18-348.3.1.el5xen ro root=/dev/mapper/sauron-c5root 8250.nr_uarts=8 xencons=off max_loop=32 irqpoll
        module /initrd-2.6.18-348.3.1.el5xen.img
                                

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