linux-kernel - [PATCH v6 28/29] x86/tsc: Restart NMI watchdog after refining tsc

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Message-Id: <20220506000008.30892-29-ricardo.neri-calderon@linux.intel.com>
Date:   Thu,  5 May 2022 17:00:07 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Cc:     Tony Luck <tony.luck@...el.com>, Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Nicholas Piggin <npiggin@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: [PATCH v6 28/29] x86/tsc: Restart NMI watchdog after refining tsc_khz

The HPET hardlockup detector relies on tsc_khz to estimate the value of
that the TSC will have when its HPET channel fires. A refined tsc_khz
helps to estimate better the expected TSC value.

Using the early value of tsc_khz may lead to a large error in the expected
TSC value. Restarting the NMI watchdog detector has the effect of kicking
its HPET channel and make use of the refined tsc_khz.

When the HPET hardlockup is not in use, restarting the NMI watchdog is
a noop.

Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: "Ravi V. Shankar" <ravi.v.shankar@...el.com>
Cc: iommu@...ts.linux-foundation.org
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: x86@...nel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Changes since v5:
 * Introduced this patch

Changes since v4
 * N/A

Changes since v3
 * N/A

Changes since v2:
 * N/A

Changes since v1:
 * N/A
---
 arch/x86/kernel/tsc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index cafacb2e58cc..cc1843044d88 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1386,6 +1386,12 @@ static void tsc_refine_calibration_work(struct work_struct *work)
 	/* Inform the TSC deadline clockevent devices about the recalibration */
 	lapic_update_tsc_freq();
 
+	/*
+	 * If in use, the HPET hardlockup detector relies on tsc_khz.
+	 * Reconfigure it to make use of the refined tsc_khz.
+	 */
+	lockup_detector_reconfigure();
+
 	/* Update the sched_clock() rate to match the clocksource one */
 	for_each_possible_cpu(cpu)
 		set_cyc2ns_scale(tsc_khz, cpu, tsc_stop);
-- 
2.17.1