Re: Dom0 bad network performance

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hi Mathew,

Am 14.02.21 um 11:11 schrieb Mathew, Cherry G.:
> hi Matthias,
>
> could you please find the interrupt rate using :
>
> # intrctl list -w 1

Thanks for the hint - I was not aware of this command. While I did not 
run my tests yet (will do later today), I just found some difference in 
the configuration here:

1) With Xen (network interface re0 assigned to ioapic)

kallisto$ intrctl list
interrupt id        CPU0  device name(s)
ioapic0 pin 9          4* acpi SCI
ioapic0 pin 18    676235* sdhc0, re0, ichsmb0
ioapic0 pin 19    280781* ahcisata0
ioapic0 pin 20        70* xhci0
ioapic0 pin 22         0* hdaudio0
ioapic0 pin 17        13* iwm0
xenev0 channel 8  548216* vcpu0 clock
xenev0 channel 9     550* xenbus0
xenev0 channel 10      0* xenevt
xenev0 channel 15 826809* xbdb1i768
xenev0 channel 16 432062* xvif1i0

2) Without Xen (network interface re0 assigned to msix4)

kallisto$ intrctl list 

interrupt id   CPU0  CPU1  device name(s)
ioapic0 pin 9     0*    0  acpi SCI
ioapic0 pin 18    5*    0  sdhc0, ichsmb0
msi0 vec 0     3311*    0  ahcisata0
msi1 vec 0       76*    0  xhci0
msi2 vec 0        0*    0  hdaudio0
msi3 vec 0       13*    0  iwm0
msix4 vec 0     180*    0  re0
ioapic0 pin 16   47*    0  i915drmkms

It has rather been pointed out before that differences between Xen and 
non-Xen are to be expected here. So that means that this is certainly no 
surprise to most.

Do I understand [1] correctly that MSI is the native interrupt handler 
for PCIe, and that using ioapic on PCIe is an emulation that may be less 
performant?

Could it be relevant to my specific problem that pin18 is shared by 
three devices of all things, one of them the network interface.

Kind regards
Matthias

[1] 
https://en.wikipedia.org/wiki/Message_Signaled_Interrupts#PCI_Express_legacy_interrupt_emulation