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Date: Fri, 13 Jul 2018 15:22:42 +0800
From: Dou Liyang <douly.fnst@...fujitsu.com>
To: Pavel Tatashin <pasha.tatashin@...cle.com>,
<steven.sistare@...cle.com>, <daniel.m.jordan@...cle.com>,
<linux@...linux.org.uk>, <schwidefsky@...ibm.com>,
<heiko.carstens@...ibm.com>, <john.stultz@...aro.org>,
<sboyd@...eaurora.org>, <x86@...nel.org>,
<linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
<tglx@...utronix.de>, <hpa@...or.com>, <peterz@...radead.org>,
<prarit@...hat.com>, <feng.tang@...el.com>, <pmladek@...e.com>,
<gnomes@...rguk.ukuu.org.uk>, <linux-s390@...r.kernel.org>,
<boris.ostrovsky@...cle.com>, <jgross@...e.com>
Subject: Re: [PATCH v13 13/18] x86/tsc: calibrate tsc only once
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@...utronix.de>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.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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