** Description changed: - == Comment: #0 - JENIFER HOPPER <jhop...@us.ibm.com> - 2018-07-12 - 11:41:50 == + [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://git.qemu.org/?p=qemu.git;a=commit;h=0c1272cc7c72dfe0ef66be8f283cf67c74b58586 + + [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 <jhop...@us.ibm.com> - 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 0c1272cc7c72dfe0ef66be8f283cf67c74b58586 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 = jhop...@us.ibm.com - + 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 = jhop...@us.ibm.com + ---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 - + + 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. + Run a workload that benefits from THP usage in a P9 KVM guest.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1781526 Title: Ubuntu18.04 - qemu patch to align memory to allow 2MB THP To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-power-systems/+bug/1781526/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
