Ubuntu18.04 - qemu patch to align memory to allow 2MB THP
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
The Ubuntu-power-systems project |
Fix Released
|
Medium
|
Unassigned | ||
qemu (Ubuntu) |
Fix Released
|
Medium
|
Unassigned | ||
Bionic |
Won't Fix
|
Medium
|
Unassigned |
Bug Description
[Impact]
* Memory on ppc64el was only aligned at pagesize, but for THP to benefit
aligning on 2MB would be beneficial for translations (performance)
[Test Case]
* It was reported that running specjbb2005 in guests on a P9 system can
gain up to 10% performance. Therefore running that with a guest that
workload (guest pinned, THP set to always) would be the test that shall
be done (on a non shared performance capable machine). IBM committed to
verify the PPA and eventually the SRU with such a setup (or
comparable).
[Fix]
* Backport https:/
[Regression Potential]
* It adds a PPC64 check for the alignment, that does not change any other
architectures (unless this one line change is wrong). The change runs
fine in later versions and is requested by IBM owning the ppc64el arch.
The effect should be just some speedup by THP being able to pick up
some more memory. As we have seen (comment #8) side effects are
possible, but all that are known are sorted out now.
[Other Info]
* This was postponed for a while as the change would have made another
issue more likely. But that is now fixed (in the kernel), so we can go
on.
--- original bug ---
== Comment: #0 - JENIFER HOPPER <email address hidden> - 2018-07-12 11:41:50 ==
---Problem Description---
We would like to request the following simple qemu patch be applied because it can provide significant performance improvements for Power9 KVM guests that benefit from 2MB THP usage:
commit 0c1272cc7c72dfe
osdep: powerpc64 align memory to allow 2MB radix THP page tables
This allows KVM with the Book3S radix MMU mode to take advantage of
THP and install larger pages in the partition scope page tables (the
host translation).
--
For instance, when THP is enabled I measured a 10% throughput improvement with this patch for a full system P9 Radix guest running the SPECjbb2005 workload.
Contact Information = <email address hidden>
---uname output---
Linux perfwsp6 4.15.0-20-generic #21-Ubuntu SMP Tue Apr 24 06:14:44 UTC 2018 ppc64le ppc64le ppc64le GNU/Linux
Machine Type = 8335-GTH
---Debugger---
A debugger is not configured
---Steps to Reproduce---
Run a workload that benefits from THP usage in a P9 KVM guest.
tags: | added: architecture-ppc64le bugnameltc-169712 severity-high targetmilestone-inin1804 |
Changed in ubuntu: | |
assignee: | nobody → Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage) |
affects: | ubuntu → qemu (Ubuntu) |
tags: | added: triage-g |
Changed in ubuntu-power-systems: | |
importance: | Undecided → High |
assignee: | nobody → Canonical Server Team (canonical-server) |
Changed in ubuntu-power-systems: | |
status: | New → Triaged |
Changed in qemu (Ubuntu): | |
assignee: | Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage) → David Britton (davidpbritton) |
Changed in qemu (Ubuntu Bionic): | |
assignee: | nobody → David Britton (davidpbritton) |
Changed in qemu (Ubuntu): | |
importance: | Undecided → High |
Changed in qemu (Ubuntu Bionic): | |
importance: | Undecided → High |
Changed in qemu (Ubuntu Bionic): | |
assignee: | David Britton (davidpbritton) → nobody |
Changed in qemu (Ubuntu): | |
assignee: | David Britton (davidpbritton) → nobody |
Changed in ubuntu-power-systems: | |
status: | Triaged → Incomplete |
Changed in ubuntu-power-systems: | |
status: | Incomplete → Won't Fix |
description: | updated |
Changed in ubuntu-power-systems: | |
status: | Won't Fix → Incomplete |
Changed in qemu (Ubuntu): | |
importance: | High → Medium |
Changed in ubuntu-power-systems: | |
assignee: | Canonical Server Team (canonical-server) → nobody |
Changed in ubuntu-power-systems: | |
status: | Incomplete → Fix Released |
Hi Jennifer,
I'll take a look putting it into the coming qemu 2.12 merge for Cosmic first (needs to be there for the SRU policy anyway). I saw that it is so new, that is isn't even in 2.12 (upstream) so I'll add it as a patch to Cosmic as well.