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    SubjectRe: [PATCH v13 13/18] x86/tsc: calibrate tsc only once
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    At 07/12/2018 08:04 AM, Pavel Tatashin wrote:
    > During boot tsc is calibrated twice: once in tsc_early_delay_calibrate(),
    > and the second time in tsc_init().
    >
    > Rename tsc_early_delay_calibrate() to tsc_early_init(), and rework it so
    > the calibration is done only early, and make tsc_init() to use the values
    > already determined in tsc_early_init().
    >
    > Sometimes it is not possible to determine tsc early, as the subsystem that
    > is required is not yet initialized, in such case try again later in
    > tsc_init().
    >
    > Suggested-by: Thomas Gleixner <tglx@linutronix.de>
    > Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>

    Hi Pavel,

    Aha, a complex solution for a simple problem! ;-) And I did find any
    benefits of doing that. did I miss something?

    As the cpu_khz and tsc_khz are global variables and the tsc_khz may
    be reset to cpu_khz. How about the following patch.

    Thanks,
    dou
    ------------------------8<-----------------------------------

    diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
    index 74392d9d51e0..e54fa1037d45 100644
    --- a/arch/x86/kernel/tsc.c
    +++ b/arch/x86/kernel/tsc.c
    @@ -1370,8 +1370,10 @@ void __init tsc_init(void)
    return;
    }

    - cpu_khz = x86_platform.calibrate_cpu();
    - tsc_khz = x86_platform.calibrate_tsc();
    + if (!tsc_khz) {
    + cpu_khz = x86_platform.calibrate_cpu();
    + tsc_khz = x86_platform.calibrate_tsc();
    + }

    /*
    * Trust non-zero tsc_khz as authorative,
    > ---
    > arch/x86/include/asm/tsc.h | 2 +-
    > arch/x86/kernel/setup.c | 2 +-
    > arch/x86/kernel/tsc.c | 86 ++++++++++++++++++++------------------
    > 3 files changed, 48 insertions(+), 42 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
    > index 2701d221583a..c4368ff73652 100644
    > --- a/arch/x86/include/asm/tsc.h
    > +++ b/arch/x86/include/asm/tsc.h
    > @@ -33,7 +33,7 @@ static inline cycles_t get_cycles(void)
    > extern struct system_counterval_t convert_art_to_tsc(u64 art);
    > extern struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns);
    >
    > -extern void tsc_early_delay_calibrate(void);
    > +extern void tsc_early_init(void);
    > extern void tsc_init(void);
    > extern void mark_tsc_unstable(char *reason);
    > extern int unsynchronized_tsc(void);
    > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
    > index 01fcc8bf7c8f..07445482bb57 100644
    > --- a/arch/x86/kernel/setup.c
    > +++ b/arch/x86/kernel/setup.c
    > @@ -1014,7 +1014,7 @@ void __init setup_arch(char **cmdline_p)
    > */
    > init_hypervisor_platform();
    >
    > - tsc_early_delay_calibrate();
    > + tsc_early_init();
    >
    > x86_init.resources.probe_roms();
    >
    > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
    > index 186395041725..bc8eb82050a3 100644
    > --- a/arch/x86/kernel/tsc.c
    > +++ b/arch/x86/kernel/tsc.c
    > @@ -33,6 +33,8 @@ EXPORT_SYMBOL(cpu_khz);
    > unsigned int __read_mostly tsc_khz;
    > EXPORT_SYMBOL(tsc_khz);
    >
    > +#define KHZ 1000
    > +
    > /*
    > * TSC can be unstable due to cpufreq or due to unsynced TSCs
    > */
    > @@ -1335,34 +1337,10 @@ static int __init init_tsc_clocksource(void)
    > */
    > device_initcall(init_tsc_clocksource);
    >
    > -void __init tsc_early_delay_calibrate(void)
    > -{
    > - unsigned long lpj;
    > -
    > - if (!boot_cpu_has(X86_FEATURE_TSC))
    > - return;
    > -
    > - cpu_khz = x86_platform.calibrate_cpu();
    > - tsc_khz = x86_platform.calibrate_tsc();
    > -
    > - tsc_khz = tsc_khz ? : cpu_khz;
    > - if (!tsc_khz)
    > - return;
    > -
    > - lpj = tsc_khz * 1000;
    > - do_div(lpj, HZ);
    > - loops_per_jiffy = lpj;
    > -}
    > -
    > -void __init tsc_init(void)
    > +static bool determine_cpu_tsc_frequncies(void)
    > {
    > - u64 lpj, cyc;
    > - int cpu;
    > -
    > - if (!boot_cpu_has(X86_FEATURE_TSC)) {
    > - setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
    > - return;
    > - }
    > + /* Make sure that cpu and tsc are not already calibrated */
    > + WARN_ON(cpu_khz || tsc_khz);
    >
    > cpu_khz = x86_platform.calibrate_cpu();
    > tsc_khz = x86_platform.calibrate_tsc();
    > @@ -1377,20 +1355,51 @@ void __init tsc_init(void)
    > else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz)
    > cpu_khz = tsc_khz;
    >
    > - if (!tsc_khz) {
    > - mark_tsc_unstable("could not calculate TSC khz");
    > - setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
    > - return;
    > - }
    > + if (tsc_khz == 0)
    > + return false;
    >
    > pr_info("Detected %lu.%03lu MHz processor\n",
    > - (unsigned long)cpu_khz / 1000,
    > - (unsigned long)cpu_khz % 1000);
    > + (unsigned long)cpu_khz / KHZ,
    > + (unsigned long)cpu_khz % KHZ);
    >
    > if (cpu_khz != tsc_khz) {
    > pr_info("Detected %lu.%03lu MHz TSC",
    > - (unsigned long)tsc_khz / 1000,
    > - (unsigned long)tsc_khz % 1000);
    > + (unsigned long)tsc_khz / KHZ,
    > + (unsigned long)tsc_khz % KHZ);
    > + }
    > + return true;
    > +}
    > +
    > +static unsigned long get_loops_per_jiffy(void)
    > +{
    > + unsigned long lpj = tsc_khz * KHZ;
    > +
    > + do_div(lpj, HZ);
    > + return lpj;
    > +}
    > +
    > +void __init tsc_early_init(void)
    > +{
    > + if (!boot_cpu_has(X86_FEATURE_TSC))
    > + return;
    > + if (!determine_cpu_tsc_frequncies())
    > + return;
    > + loops_per_jiffy = get_loops_per_jiffy();
    > +}
    > +
    > +void __init tsc_init(void)
    > +{
    > + if (!boot_cpu_has(X86_FEATURE_TSC)) {
    > + setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
    > + return;
    > + }
    > +
    > + if (!tsc_khz) {
    > + /* We failed to determine frequencies earlier, try again */
    > + if (!determine_cpu_tsc_frequncies()) {
    > + mark_tsc_unstable("could not calculate TSC khz");
    > + return;
    > + }
    > }
    >
    > /* Sanitize TSC ADJUST before cyc2ns gets initialized */
    > @@ -1413,10 +1422,7 @@ void __init tsc_init(void)
    > if (!no_sched_irq_time)
    > enable_sched_clock_irqtime();
    >
    > - lpj = ((u64)tsc_khz * 1000);
    > - do_div(lpj, HZ);
    > - lpj_fine = lpj;
    > -
    > + lpj_fine = get_loops_per_jiffy();
    > use_tsc_delay();
    >
    > check_system_tsc_reliable();
    >


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