Red Hat Bugzilla – Bug 390451
Pick up paging performance improvements from upstream Xen
Last modified: 2011-07-21 06:27:51 EDT
Upstream Xen-3.1 contains the following in changeset 14731:
> # HG changeset patch
> # User email@example.com
> # Date 1175760633 -3600
> # Node ID 14c25e48a55730115c71e592ae065e715c1d23af
> # Parent 07d3208c0ca3b6e746745d2bc08f7aa12ed39269
> linux: improve x86 page table handling performance
> Where possible,
> - use hypercalls instead of writing to read-only pages
> - fold TLB flushes into page table update hypercalls
> - on PAE, use single-access updates instead of two-access ones
> The single change to PAE pte_clear() yields a 25-30% boost for kernel
> builds on a 4x2x2 CPUs, 8Gb box; the other changes together yield
> improvements of 2-5%.
Note that it also needs the bugfixes from upstream linux-2.6.18-xen.hg's csets
265 and 266.
Given the magnitude of the performance improvement quoted, we should at least
evaluate this for 5.2.
Missed the boat for RHEL 5.2, flaged to look at for 5.3.
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux maintenance release. Product Management has requested
further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products. This request is not yet committed for inclusion in an Update
Created attachment 465972 [details]
I think backporting the whole series is pretty much out of question at this point.
However, if the pte_clear hunk is really that effective, it may be worthwhile to benchmark it.
Measured 2-3% improvement on a 2 VCPU RHEL5 32-bit guest running on 64-bit host
Patch(es) available in kernel-2.6.18-248.el5
Detailed testing feedback is always welcomed.
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.