realtime: set tsc as reliable

resolves: rhbz#2086374

tuned-2.18.0-realtime-tsc-reliable.patch

@@ -0,0 +1,45 @@
+From 49cc817871672d0a5bad138dd7ad781b684a9fd9 Mon Sep 17 00:00:00 2001
+From: Nicolas Saenz Julienne <nsaenzju@redhat.com>
+Date: Wed, 16 Mar 2022 17:06:45 +0100
+Subject: [PATCH] realtime: Set tsc as 'reliable'
+
+We already disable the clocksource watchdog, it's there to double-check
+whether clock results are coherent between reads. But a new reliability
+test was introduced in recent kernels[1], tracking tsc drift between
+CPUs[2]. It works by programming timers on all CPUs, including isolated
+ones, and checks whether the tsc was adjusted in between runs. This
+introduces unwarranted latency on real time systems. So let's promote
+tsc to 'reliable', which disables both checks.
+
+There shouldn't be any impact on old nor new setups. First, this test
+didn't exist in the past, so any eventual drift was left uncorrected.
+Second, most telco and HPC use-cases will make heavy use of tsc in
+user-space, and its reliability is already assumed in the system's
+design.
+
+[1] c7719e793478 x86/tsc: Add a timer to make sure TSC_adjust is always
+		 checked
+[2] Generally caused by rogue BIOSes adjusting the tsc on a CPU and not
+    doing so on the rest
+
+Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
+---
+ profiles/realtime/tuned.conf | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/profiles/realtime/tuned.conf b/profiles/realtime/tuned.conf
+index b1657af..196ed01 100644
+--- a/profiles/realtime/tuned.conf
++++ b/profiles/realtime/tuned.conf
+@@ -52,7 +52,7 @@ kernel.timer_migration = 0
+ /sys/devices/system/machinecheck/machinecheck*/ignore_ce = 1
+ 
+ [bootloader]
+-cmdline_realtime=+isolcpus=${managed_irq}${isolated_cores} intel_pstate=disable nosoftlockup tsc=nowatchdog
++cmdline_realtime=+isolcpus=${managed_irq}${isolated_cores} intel_pstate=disable nosoftlockup tsc=reliable
+ 
+ [irqbalance]
+ banned_cpus=${isolated_cores}
+-- 
+2.35.1
+

tuned.spec

@@ -35,7 +35,7 @@
 Summary: A dynamic adaptive system tuning daemon
 Name: tuned
 Version: 2.18.0
-Release: 1%{?prerel1}%{?dist}
+Release: 2%{?prerel1}%{?dist}
 License: GPLv2+
 Source0: https://github.com/redhat-performance/%{name}/archive/v%{version}%{?prerel2}/%{name}-%{version}%{?prerel2}.tar.gz
 # RHEL-9 specific recommend.conf:
@@ -97,6 +97,7 @@ Recommends: subscription-manager
 Requires: python3-syspurpose
 %endif
 %endif
+Patch0: tuned-2.18.0-realtime-tsc-reliable.patch
 
 %description
 The tuned package contains a daemon that tunes system settings dynamically.
@@ -548,6 +549,10 @@ fi
 %{_mandir}/man7/tuned-profiles-openshift.7*
 
 %changelog
+* Thu May 19 2022 Jaroslav Škarvada <jskarvad@redhat.com> - 2.18.0-2
+- realtime: set tsc as reliable
+  resolves: rhbz#2086374
+
 * Wed Feb  9 2022 Jaroslav Škarvada <jskarvad@redhat.com> - 2.18.0-1
 - new release
   - rebased tuned to latest upstream