http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=100371...
Excellent article above describing how to fix this in 3.5, still valid for 4
"Determining if IRQ Sharing Issues Affect Your System's Performance
+The tell-tale sign of IRQ sharing
between VMkernel and the service console is a high number of interrupts
being serviced by PCPU0 (CPU #0 on the physical host) while the other
CPUs are relatively lightly loaded. The high interrupt rates might
sometimes render the service console unusable and cause a high
variation in ESX Server performance.+
+The most common service console device
that causes IRQ sharing is the USB controller. On the VMkernel side,
the network and storage controllers are susceptible to IRQ sharing. IRQ
sharing is more common in dual- and quad-port NICs and storage HBAs
than in single port controllers. However, IRQ sharing is not restricted
only to these devices. The effect is more visible under I/O intensive
loads (with high interrupt rates). The problem might manifest itself as
variation in performance or as an absolute drop in ESX Server
performance.+
+To determine if your setup suffers
from IRQ sharing, list the IRQ assignment in VMkernel by typing the
following at the command-line of the service console:+
> cat /proc/vmware/interrupts
This lists the interrupt usage. The output looks similar to the following example:
+Vector PCPU 0 PCPU 1 PCPU 2 PCPU 3
0x21: 0 0 0 0 VMK ACPI Interrupt
0x29: 1 0 0 0 <COS irq 1 (ISA edge)>, VMK keyboard
0x31: 4 0 0 0 <COS irq 3 (ISA edge)>
0x39: 4 0 0 0 <COS irq 4 (ISA edge)>
0x41: 0 0 0 0 <COS irq 6 (ISA edge)>
0x49: 0 0 0 0 <COS irq 7 (ISA edge)>
0x51: 0 0 0 0 <COS irq 8 (ISA edge)>
0x59: 0 0 0 0 <COS irq 12 (ISA edge)>
0x61: 0 0 0 0 <COS irq 13 (ISA edge)>
0x69: 43762 0 0 0 COS irq 14 (ISA edge)
0x71: 0 0 0 0 <COS irq 15 (ISA edge)>
0x79: 7917 542 3583 8292 <COS irq 16 (PCI level)>, VMK aic79xx
0x81: 1544 0 0 0 COS irq 17 (PCI level), VMK aic79xx
0x89: 1212177 0 0 0 COS irq 19 (PCI level), VMK vmnic1
0x91: 90997 0 0 0 COS irq 18 (PCI level), VMK vmnic0
0x99: 152 0 0 0 <COS irq 20 (PCI level)>, VMK qla2300
0xdf: 8904447 10869326 11006262 10844861 VMK timer
0xe1: 74 5582 12007 16005 VMK monitor
0xe9: 60854 443843 477389 509724 VMK resched
0xec: 0 0 0 0 VMK ucodeUpdate
0xf1: 3 40 68 100 VMK tlb
0xf9: 243265 0 0 0 VMK noop
0xfc: 0 0 0 0 VMK thermal
0xfd: 0 0 0 0 VMK lint1
0xfe: 0 0 0 0 VMK error
0xff: 0 0 0 0 VMK spurious
++This output lists the interrupt vectors with the number of interrupts fielded by each physical CPU ( PCPU).
The last column lists the device or devices associated with the
particular IRQs. Along with the device name, the owner of the device is
also listed. COS refers to service console ownership, and VMK refers to VMkernel ownership. (In older versions of ESX Server, the service console was named the console operating system, or COS.)+
+For
the sake of analysis, you can ignore devices owned by the service
console that have their names enclosed in angle brackets (<>),
because the service console does not load a driver for them. All other
interrupt vectors that have a device with COS and VMK next to them
indicate the IRQs are shared for that device. Again, devices with low
interrupt rates (for example, 0x81 and 0x99) can be ignored because the
performance impact due to them is minimal.+
+In the above example, IRQ 0x81, 0x89,
0x91, and 0x99 are shared between service-console and VMK devices. You
don't need to analyze the interrupt counts for 0x81 and 0x99, because
the counts are reasonably low. Also note that all interrupts for these
four IRQs are being fielded by PCPU 0, while all other PCPUs show zero
interrupt count. In contrast, interrupt vectors 0x89 and 0x91 (for
vmnic1 and vmnic0) show high interrupt counts. The shared IRQs in the
service console for vmnic1 and vmnic0 are IRQ 19 and IRQ 18
respectively.+
+In this example, you need to remove
the device conflicting with vmnic0 and vmnic1 from the service console.
To find the offending device in the service console, list the interrupt
vectors:+
> cat /proc/interrupts
This lists the IRQ lines assigned to the devices in the service console.
+CPU0
0: 1744046 vmnix-edge timer
1: 3 vmnix-edge keyboard
2: 163071 vmnix-edge VMnix interrupt
14: 44022 vmnix-edge ide0
17: 1499 vmnix-level usb-uhci, ehci-hcd
18: 91236 vmnix-level usb-uhci
19: 1303228 vmnix-level usb-uhci
NMI: 0
LOC: 0
ERR: 0
MIS: 0
+You can see that both IRQ 18 and IRQ 19 are in use by usb-uhci, a USB Universal Host Controller device."
https://virtual-simon.co.uk/
