Re: tip.today - scheduler bam boom crash (cpu hotplug)

Paolo Bonzini
2017-02-27T17:27:58Z

On 27/02/2017 17:36, Peter Zijlstra wrote:
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 4e95b2e0d95f..bc3bbb6a8ab0 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -555,10 +555,8 @@ static void early_init_amd(struct cpuinfo_x86 *c)
> if (c->x86_power & (1 << 8)) {
> set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
> set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
> - if (check_tsc_unstable())
> - clear_sched_clock_stable();
> } else {
> - clear_sched_clock_stable();
> + mark_tsc_unstable("not invariant");
> }
>
> /* Bit 12 of 8000_0007 edx is accumulated power mechanism. */
> diff --git a/arch/x86/kernel/cpu/centaur.c b/arch/x86/kernel/cpu/centaur.c
> index 2c234a6d94c4..0fdff183aa30 100644
> --- a/arch/x86/kernel/cpu/centaur.c
> +++ b/arch/x86/kernel/cpu/centaur.c
> @@ -105,7 +105,7 @@ static void early_init_centaur(struct cpuinfo_x86 *c)
> set_cpu_cap(c, X86_FEATURE_SYSENTER32);
> #endif
>
> - clear_sched_clock_stable();
> + mark_tsc_unstable("not invariant");
> }
>
> static void init_centaur(struct cpuinfo_x86 *c)
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index f07005e6f461..2b7ff648ea25 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -86,7 +86,7 @@ static void default_init(struct cpuinfo_x86 *c)
> strcpy(c->x86_model_id, "386");
> }
> #endif
> - clear_sched_clock_stable();
> + mark_tsc_unstable("not invariant");
> }
>
> static const struct cpu_dev default_cpu = {
> @@ -1076,7 +1076,7 @@ static void identify_cpu(struct cpuinfo_x86 *c)
> if (this_cpu->c_init)
> this_cpu->c_init(c);
> else
> - clear_sched_clock_stable();
> + mark_tsc_unstable("not invariant");
>
> /* Disable the PN if appropriate */
> squash_the_stupid_serial_number(c);
> diff --git a/arch/x86/kernel/cpu/cyrix.c b/arch/x86/kernel/cpu/cyrix.c
> index 47416f959a48..35057d67e864 100644
> --- a/arch/x86/kernel/cpu/cyrix.c
> +++ b/arch/x86/kernel/cpu/cyrix.c
> @@ -184,7 +184,7 @@ static void early_init_cyrix(struct cpuinfo_x86 *c)
> set_cpu_cap(c, X86_FEATURE_CYRIX_ARR);
> break;
> }
> - clear_sched_clock_stable();
> + mark_tsc_unstable("not invariant");
> }
>
> static void init_cyrix(struct cpuinfo_x86 *c)
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index 017ecd3bb553..e0e192e43a4c 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -161,10 +161,8 @@ static void early_init_intel(struct cpuinfo_x86 *c)
> if (c->x86_power & (1 << 8)) {
> set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
> set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
> - if (check_tsc_unstable())
> - clear_sched_clock_stable();
> } else {
> - clear_sched_clock_stable();
> + mark_tsc_unstable("not invariant");
> }
>
> /* Penwell and Cloverview have the TSC which doesn't sleep on S3 */

Doh, these are called _before_ kvmclock_init. But perhaps they can all
be replaced by something like this:

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 2724dc82f992..3080b6877190 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1398,6 +1398,9 @@ void __init tsc_init(void)

use_tsc_delay();

+ if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
+ mark_tsc_unstable("not invariant");
+
if (unsynchronized_tsc())
mark_tsc_unstable("TSCs unsynchronized");

The rest seems nice.

Paolo