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Re: [PATCH] target/s390x/kvm: Enable adapter interruption suppression ag

From: Matthew Rosato
Subject: Re: [PATCH] target/s390x/kvm: Enable adapter interruption suppression again
Date: Thu, 16 Jan 2020 09:51:37 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0

On 1/16/20 8:22 AM, Christian Borntraeger wrote:

On 16.01.20 13:55, Thomas Huth wrote:
On 16/01/2020 13.50, Cornelia Huck wrote:
On Thu, 16 Jan 2020 13:20:26 +0100
Thomas Huth <address@hidden> wrote:

The AIS feature has been disabled late in the v2.10 development
cycle since there were some issues with migration (see commit
3f2d07b3b01ea61126b - "s390x/ais: for 2.10 stable: disable ais
facility"). We originally wanted to enable it again for newer
machine types, but apparently we forgot to do this so far. Let's
do it for the new s390-ccw-virtio-5.0 machine now.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1756946
Signed-off-by: Thomas Huth <address@hidden>
  hw/s390x/s390-virtio-ccw.c         |  4 ++++
  include/hw/s390x/s390-virtio-ccw.h |  4 ++++
  target/s390x/kvm.c                 | 11 ++++++++---
  3 files changed, 16 insertions(+), 3 deletions(-)

@@ -365,10 +367,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
       * The migration interface for ais was introduced with kernel 4.13
       * but the capability itself had been active since 4.12. As migration
-     * support is considered necessary let's disable ais in the 2.10
-     * machine.
+     * support is considered necessary we only enable this for newer

s/necessary we only enable this/necessary, we only try to enable this/

+     * machine types and if KVM_CAP_S390_AIS_MIGRATION is available.

maybe s/and if/if/

Sure ... could you fix it up when picking up the patch (in case I don't
have to respin), or do you want me to send a v2?

-    /* kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0); */
+    if (smc->kvm_ais_allowed &&
+        kvm_check_extension(s, KVM_CAP_S390_AIS_MIGRATION)) {
+        kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0);
+    }
      return 0;

Looks good.

Remind me again: ais only made a difference for pci devices, right? Is
it enough to give this a quick whirl with virtio-pci devices?

I don't remember the details, Christian, could you please answer this

Yes, IIRC AIS was there for PCI, but not for Crypto or virtio.

This matches my understanding as well.

The patch looks sane, but it would be good if someone could try
the AIS stuff.

Matt, can you have a look?

Sure. But my PCI environment is currently down for a maintenance window, will try again later today.

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