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