Problem Description ------------------- Intel "transactional synchronization Extensions" (TSX) hardware feature was disabled by default in RHEL-8.3[1] kernel, specifically from kernel-4.18.0-214.el8 onwards. This was done to address performance penalty of "TAA" (TSX Asynchronous Abort) mitigations on Intel Cascadelke servers. However, as an undesirable side-effect, it breaks forward live migration compatibility of libvirt-based KVM guests — e.g. when migrating a guest from RHEL-7.9 to RHEL-8.3 (or from RHEL-8.2 to RHEL-8.3). We need to document this fallout for OSP. Including the TripleO work that is being done in this area[3]. This affects the following scenarios: - Major upgrade from OSP-13 to OSP-16.2 - Minor _update_ from OSP-16.1 to OSP-16.2 - New OSP 16.2 deployments References ---------- [1] https://bugzilla.redhat.com/show_bug.cgi?id=1828642 — kernel: Disable Intel TSX by default on newer CPUs [2] https://bugzilla.redhat.com/show_bug.cgi?id=1923118 — [kernel] "redhat/configs: Change Intel TSX default to off" breaks live migration of KVM guests [3] https://bugzilla.redhat.com/show_bug.cgi?id=1923165 — [OSP-16.2] [Upgrades][TripleO] Add a config to disable Intel "TSX" on RHEL-8.3 kernel
This is now taken care of here[1] (but _again_ needs updating -- see further below): That said, right after publishing the above, Intel came up with a CPU microcode update to disable TSX in the hardware: https://access.redhat.com/articles/6101171 Intel June 2021 Microcode Update In the above update, in the "Transactional Synchronization Extension (TSX) Deprecation" section, it says: "... update disables TSX by default on some platforms" Which is most likely to mean: The TSX flags ('hle' and 'rtm') won't show up in /proc/cpuinfo anymore on hosts that have applied this CPU microcode. So we need to update the KBase[1] and also OSP documentation potentially... [1] https://access.redhat.com/solutions/6036141 — Guidance on Intel TSX impact on OpenStack guests (applies for RHEL 8.3 and above)
Hi Kashyap, Thank you for opening this ticket! I have actually started working on a draft to document the fact that the TSX feature is now disable by default starting with RHEL 8.3: * in BZ#1975450 (related eng BZ#1975240) for the 'Keeping Red Hat OpenStack Platform Updated' doc * and BZ#1975448 for the 'Framework for Upgrades (13 to 16.1)' doc I will link this BZ with the other two. Many thanks, Vlada
Closing this ticket as the content changes required for this BZ have been addressed in the following bugs. Please feel free to reopen the ticket if you think that more changes are necessary for the 16.2 OSP docs. Thank you (In reply to Vlada Grosu from comment #3) > Hi Kashyap, > > Thank you for opening this ticket! > > I have actually started working on a draft to document the fact that the TSX > feature is now disable by default starting with RHEL 8.3: > > * in BZ#1975450 (related eng BZ#1975240) for the 'Keeping Red Hat OpenStack > Platform Updated' doc > > * and BZ#1975448 for the 'Framework for Upgrades (13 to 16.1)' doc > > I will link this BZ with the other two. > > Many thanks, > Vlada