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Subject: Re: [RFC] x86, tsc: Add kcmdline args for skipping tsc calibration
 sequences
To:     Prarit Bhargava <prarit@redhat.com>,
        "Brown, Len" <len.brown@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     "mingo@kernel.org" <mingo@kernel.org>,
        "Du, Alek" <alek.du@intel.com>,
        "arjan@linux.intel.com" <arjan@linux.intel.com>,
        "Tang, Feng" <feng.tang@intel.com>
References: <fdf96605-a4a0-049b-51c9-1e68cc2a9b93@supermicro.com>
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From:   patrickg <patrickg@supermicro.com>
Message-ID: <f718c935-d5b4-111d-abe1-e7a61d08237b@supermicro.com>
Date:   Thu, 25 Oct 2018 12:13:26 -0700
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Sorry for the delay; lkml folder sorting gone wrong.

On 10/25/18 11:01 AM, Prarit Bhargava wrote:
> Patrick can you reply back with the entire patch

Yes; watch the editor bork it even more than it originally did, though.


---Copypasta of first RFC patch---

---
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 74392d9..5a07d12 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -47,6 +47,13 @@ static DEFINE_STATIC_KEY_FALSE(__use_tsc);
 
 int tsc_clocksource_reliable;
 
+/*
+ * TSC calibration sequence disablement
+ */
+int calibrate_cpuid_khz_disabled = 0;
+int calibrate_msr_disabled = 0;
+int calibrate_quick_disabled = 0;
+
 static u32 art_to_tsc_numerator;
 static u32 art_to_tsc_denominator;
 static u64 art_to_tsc_offset;
@@ -281,6 +288,32 @@ static int __init tsc_setup(char *str)
 
 __setup("tsc=", tsc_setup);
 
+static int __init setup_tsc_calibration_order(char *str)
+{
+        if (!str)
+                return -EINVAL;
+
+        while (*str) {
+                if (!strncmp(str, "nocpuid", 7)) {
+                        calibrate_cpuid_khz_disabled = 1;
+                        pr_info("TSC CPUID khz calibrate disabled\n");
+                } else if (!strncmp(str, "nomsr", 5)) {
+                        calibrate_msr_disabled = 1;
+                        pr_info("TSC msr calibrate disabled\n");
+                } else if (!strncmp(str, "noquick", 7)) {
+                        calibrate_quick_disabled = 1;
+                        pr_info("TSC quick calibrate disabled\n");
+                }
+
+                str += strcspn(str, ",");
+                while (*str == ',')
+                        str++;
+        }
+        return 1;
+}
+
+__setup("tsc_calibrate=", setup_tsc_calibration_order);
+
 #define MAX_RETRIES     5
 #define SMI_TRESHOLD    50000
 
@@ -675,19 +708,25 @@ unsigned long native_calibrate_cpu(void)
         unsigned long flags, latch, ms, fast_calibrate;
         int hpet = is_hpet_enabled(), i, loopmin;
 
-        fast_calibrate = cpu_khz_from_cpuid();
-        if (fast_calibrate)
-                return fast_calibrate;
+        if (!calibrate_cpuid_khz_disabled) {
+                fast_calibrate = cpu_khz_from_cpuid();
+                if (fast_calibrate)
+                        return fast_calibrate;
+        }
 
-        fast_calibrate = cpu_khz_from_msr();
-        if (fast_calibrate)
-                return fast_calibrate;
+        if (!calibrate_msr_disabled) {
+                fast_calibrate = cpu_khz_from_msr();
+                if (fast_calibrate)
+                        return fast_calibrate;
+        }
 
-        local_irq_save(flags);
-        fast_calibrate = quick_pit_calibrate();
-        local_irq_restore(flags);
-        if (fast_calibrate)
-                return fast_calibrate;
+        if (!calibrate_quick_disabled) {
+                local_irq_save(flags);
+                fast_calibrate = quick_pit_calibrate();
+                local_irq_restore(flags);
+                if (fast_calibrate)
+                        return fast_calibrate;
+        }
 
         /*
          * Run 5 calibration loops to get the lowest frequency value
---