[21.10 FEAT] zKVM: Spinlock Yield Forwarding

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In a spinlock situation DIAG 9C is used by Linux to yield a CPU if it detects that the CPU is not running via SIGP Sense Running. In KVM it can happen that the VCPU is running but its backing thread is scheduled on a host CPU that is not running itself. In this case the host should issue a DIAG 9C for this CPU.

Value: Better overall performance due to reduced lock contention.

Feature will be provided via kernel >= 5.11

[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2021-02-23 03:49 EDT-------
Feature will not make it into 21.04, Moved to 21.10

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]

[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2021-08-12 07:50 EDT-------
@Canonical (Frank): Fix is available as part of kernel 5.13.
Here's the commit ID:

87e28a15 KVM: s390: diag9c (directed yield) forwarding

[Frank Heimes (fheimes)]

Thx Boris for sharing the commit.
Its already in as
87e28a15c42c KVM: s390: diag9c (directed yield) forwarding
and 5.13 is currently in -proposed, hence I update the the ticket to Fix Committed.

[Frank Heimes (fheimes)]

Meanwhile Kernel 5.13 landed in impish-release:
linux-generic | 5.13.0.14.25 | impish
hence closing this ticket with Fix Released.

[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2021-10-25 05:54 EDT-------
Fix landed in impish (U21.10), hence closing the bug.
IBM BZ status change to:->CLOSED