[pve-devel] [PATCH pve-ceph] fix compatibility with CPUs not supporting SSE 4.1 instructions

[Stefan Hanreich]

One of our users ran into issues with running Ceph on older CPU
architectures [1]. This is apparently due to a bug in gcc-12 that
leads to SSE 4.1 instructions always being executed rather than
dynamically dispatching functions using those instructions. Those
binaries then break on older CPUs that do not support this instruction
set.

I've ran some benchmarks with `rados bench` against our last release
(18.2.0-pve2) and this new version. The commands were taken from our
latest Ceph benchmarking paper [2]. The results showed that this patch
does not lead to performance regressions on newer hardware.

                  18.2.0-pve2    this patch
Read EC           4574.28        4651.95
Write EC          3739.59        3773.87
Read Replicated   5345.34        5568.41
Write Replicated  4123.28        4066.19
(numbers correspond to bandwidth in MB/s)

[1] https://forum.proxmox.com/threads/proxmox-8-ceph-quincy-monitor-no-longer-working-on-amd-opteron-2427.129613
[2] https://www.proxmox.com/en/downloads/proxmox-virtual-environment/documentation/proxmox-ve-ceph-benchmark-2020-09

Signed-off-by: Stefan Hanreich <s.hanreich at proxmox.com>
---
 ...y-with-CPUs-not-supporting-SSE-4.1-i.patch | 32 +++++++++++++++++++
 patches/series                                |  1 +
 2 files changed, 33 insertions(+)
 create mode 100644 patches/0015-fix-compatibility-with-CPUs-not-supporting-SSE-4.1-i.patch

diff --git a/patches/0015-fix-compatibility-with-CPUs-not-supporting-SSE-4.1-i.patch b/patches/0015-fix-compatibility-with-CPUs-not-supporting-SSE-4.1-i.patch
new file mode 100644
index 000000000..a44aefafb
--- /dev/null
+++ b/patches/0015-fix-compatibility-with-CPUs-not-supporting-SSE-4.1-i.patch
@@ -0,0 +1,32 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Stefan Hanreich <s.hanreich at proxmox.com>
+Date: Fri, 15 Sep 2023 16:55:02 +0200
+Subject: [PATCH] fix compatibility with CPUs not supporting SSE 4.1
+ instructions
+
+Building without -O1 causes gcc-12 to emit SSE 4.1 instructions which
+are not supported on older CPU architectures. This leads to Ceph
+crashing on older CPU architectures. -O1 causes those optimizations to
+be implemented manually via runtime dispatch.
+
+Signed-off-by: Stefan Hanreich <s.hanreich at proxmox.com>
+---
+ src/erasure-code/jerasure/CMakeLists.txt | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/erasure-code/jerasure/CMakeLists.txt b/src/erasure-code/jerasure/CMakeLists.txt
+index f9cd22e11..b0a355235 100644
+--- a/src/erasure-code/jerasure/CMakeLists.txt
++++ b/src/erasure-code/jerasure/CMakeLists.txt
+@@ -67,7 +67,7 @@ endif()
+ 
+ add_library(gf-complete_objs OBJECT ${gf-complete_srcs})
+ set_target_properties(gf-complete_objs PROPERTIES 
+-  COMPILE_FLAGS "${SIMD_COMPILE_FLAGS}")
++  COMPILE_FLAGS "${SIMD_COMPILE_FLAGS} -O1")
+ set_target_properties(gf-complete_objs PROPERTIES 
+   COMPILE_DEFINITIONS "${GF_COMPILE_FLAGS}")
+ 
+-- 
+2.39.2
+
diff --git a/patches/series b/patches/series
index c78de0235..df9d7baf6 100644
--- a/patches/series
+++ b/patches/series
@@ -12,3 +12,4 @@
 0012-fix-4759-run-ceph-crash-daemon-with-www-data-group-f.patch
 0013-d-rules-compile-with-gcc-12.patch
 0014-debian-add-missing-bcrypt-to-manager-.requires.patch
+0015-fix-compatibility-with-CPUs-not-supporting-SSE-4.1-i.patch
-- 
2.39.2