Note: This bug is displayed in read-only format because
the product is no longer active in Red Hat Bugzilla.
RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.
DescriptionLuiz Capitulino
2018-03-12 17:37:37 UTC
Description of problem:
I can observe that the vCPU thread of the guest ran by run-tscdeadline-latency.sh is going to userspace to do I/O. This increases the latency when trying to find the best timer advancement value from the host profile. Passing tsc-deadline=on in -cpu seems to fix this. I believe that qemu is not using the in kernel irqchip if tsc-deadline=on is not passed.
Version-Release number of selected component (if applicable): tuned-2.9.0-1.el7.noarch
How reproducible:
Unfortunately, the most reliable method to reproduce is a bit complex:
1. Clone kvm-unit-tests repo:
# git clone git://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git
2. Edit x86/tscdeadline_latency.c and change TABLE_SIZE to be 1000000
3. Build it with make
4. Edit /usr/lib/tuned/realtime-virtual-host/run-tscdeadline-latency.sh and change the following line:
-kernel /usr/share/qemu-kvm/tscdeadline_latency.flat
to be:
-kernel /path/to/kvm-unit-tests/x86/tscdeadline_latency.flat
5. Run run-tscdeadline-latency.sh from the host profile
6. Trace for kvm_userspace_exit in all CPUs (make sure there are no other guests running)
Actual results:
You'll see the kvm_userspace_exit event triggering all the time.
Expected results:
There may be some kvm_userspace_exit in the beginning, but they eventually stop.
Additional info:
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2019:3633