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Re: XIVE VFIO kernel resample failure in INTx mode under heavy load

From: Cédric Le Goater
Subject: Re: XIVE VFIO kernel resample failure in INTx mode under heavy load
Date: Thu, 14 Apr 2022 14:41:26 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0

After re-reading what I just wrote, I am leaning towards disabling use of 
KVM_CAP_IRQFD_RESAMPLE as it seems last worked on POWER8 and never since :)

Did I miss something in the picture (hey Cedric)?

How about disabling it like this?

diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
index 5bfd4aa9e5aa..c999f7b1ab1b 100644
--- a/hw/ppc/spapr_pci.c
+++ b/hw/ppc/spapr_pci.c
@@ -732,7 +732,7 @@ static PCIINTxRoute spapr_route_intx_pin_to_irq(void 
*opaque, int pin)
      SpaprPhbState *sphb = SPAPR_PCI_HOST_BRIDGE(opaque);
      PCIINTxRoute route;

-    route.mode = PCI_INTX_ENABLED;
+    route.mode = PCI_INTX_DISABLED;


I like it.

You now know how to test all the combinations :) Prepare your matrix,
variables are :

 * Host OS              POWER8, POWER9+
 * KVM device           XICS (P8), XICS-on-XIVE (P9), XIVE-on-XIVE (P9)
 * kernel_irqchip       off, on
 * ic-mode              xics, xive
 * Guest OS             msi or nomsi

Ideally you should check TCG, but that's like kernel_irqchip=off.



(btw what the heck is PCI_INTX_INVERTED for?)


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