This bug is awaiting verification that the linux-intel/6.17.0-1006.6
kernel in -proposed solves the problem. Please test the kernel and
update this bug with the results. If the problem is solved, change the
tag 'verification-needed-questing-linux-intel' to 'verification-done-
questing-linux-intel'. If the problem still exists, change the tag
'verification-needed-questing-linux-intel' to 'verification-failed-
questing-linux-intel'.
If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.
See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
to enable and use -proposed. Thank you!
** Tags added: kernel-spammed-questing-linux-intel-v2 verification-needed-questing-linux-intel
--
You received this bug notification because you are subscribed to linux
in Ubuntu.
Matching subscriptions: Bgg, Bmail, Nb
https://bugs.launchpad.net/bugs/2132317
Title:
[UBUNTU 24.04] KVM: s390: improve interrupt cpu for wakeup
Status in Ubuntu on IBM z Systems:
Fix Committed
Status in linux package in Ubuntu:
Fix Committed
Status in linux source package in Noble:
Fix Committed
Status in linux source package in Plucky:
Won't Fix
Status in linux source package in Questing:
Fix Committed
Status in linux source package in Resolute:
Fix Committed
Bug description:
[ Impact ]
Commit 352ccf890a3e (KVM: s390: improve interrupt cpu for wakeup)
addresses a performance optimization in the KVM subsystem
for the s390 architecture, specifically concerning the selection
of target virtual CPUs (vCPUs) for floating interrupt delivery.
The modification changes the heuristic algorithm used to determine
which vCPU should be awakened when a floating interrupt arrives,
shifting from an idle-CPU-preference strategy to a
last-sleep-CPU-preference strategy.
This algorithmic change yields significant performance improvements
by reducing inter-processor interrupt overhead
and improving cache locality.
[ Fix ]
Backport 352ccf890a3e (KVM: s390: improve interrupt cpu for wakeup)
from mainline.
[ Test Plan ]
To test the patch it is possible to run I/O-intensive workloads
(fio, uperf) with varying vCPU configurations, on a s390x machine,
to ensure interrupt delivery remains correct without errors,
timeouts, or kernel warnings. Moreover, during I/O-intensive workloads
a performance improvement should be visible.
[ Regression Potential]
The patch modifies interrupt delivery heuristics within s390 KVM
but does not change core interrupt handling logic
or data structures significantly.
The primary risk is suboptimal vCPU selection in workload patterns
that differ from the tested scenarios (fio, uperf), potentially
causing performance regressions rather than functional failures.
---
352ccf890a3e91f58bc32503f9afdc161bc2c34a
-------------------------
KVM: s390: improve interrupt cpu for wakeup
Turns out that picking an idle CPU for floating interrupts has some
negative side effects. The guest will keep the IO workload on its CPU
and rather use an IPI from the interrupt CPU instead of moving workload.
For example a guest with 2 vCPUs and 1 fio process might run that fio on
vcpu1. If after diag500 both vCPUs are idle then vcpu0 is woken up. The
guest will then do an IPI from vcpu0 to vcpu1.
So lets change the heuristics and prefer the last CPU that went to
sleep. This one is likely still in halt polling and can be woken up
quickly.
This patch shows significant improvements in terms of bandwidth or
cpu consumption for fio and uperf workloads and seems to be a net
win.
Link: https://lore.kernel.org/linux-s390/20250904113927.119306-1-borntraeger@linux.ibm.com/
Reviewed-by: Christoph Schlameu? <schlameuss@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu-z-systems/+bug/2132317/+subscriptions
Комментариев нет:
Отправить комментарий