From: Peter Zijlstra <peterz@infradead.org>
To: Valentin Schneider <vschneid@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
linux-arch@vger.kernel.org, x86@kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Arnd Bergmann <arnd@arndb.de>, Jason Baron <jbaron@akamai.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ard Biesheuvel <ardb@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Feng Tang <feng.tang@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Mike Rapoport (IBM)" <rppt@kernel.org>,
Vlastimil Babka <vbabka@suse.cz>,
David Hildenbrand <david@redhat.com>,
"ndesaulniers@google.com" <ndesaulniers@google.com>,
Michael Kelley <mikelley@microsoft.com>,
"Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Subject: Re: [PATCH 5/5] x86/tsc: Make __use_tsc __ro_after_init
Date: Mon, 4 Dec 2023 19:20:43 +0100 [thread overview]
Message-ID: <20231204182043.GB7299@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <xhsmhcyvlc3mi.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
On Mon, Dec 04, 2023 at 05:51:49PM +0100, Valentin Schneider wrote:
> On 20/11/23 13:05, Peter Zijlstra wrote:
> > On Mon, Nov 20, 2023 at 11:55:28AM +0100, Valentin Schneider wrote:
> >> __use_tsc is only ever enabled in __init tsc_enable_sched_clock(), so mark
> >> it as __ro_after_init.
> >>
> >> Signed-off-by: Valentin Schneider <vschneid@redhat.com>
> >> ---
> >> arch/x86/kernel/tsc.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> >> index 15f97c0abc9d0..f19b42ea40573 100644
> >> --- a/arch/x86/kernel/tsc.c
> >> +++ b/arch/x86/kernel/tsc.c
> >> @@ -44,7 +44,7 @@ EXPORT_SYMBOL(tsc_khz);
> >> static int __read_mostly tsc_unstable;
> >> static unsigned int __initdata tsc_early_khz;
> >>
> >> -static DEFINE_STATIC_KEY_FALSE(__use_tsc);
> >> +static DEFINE_STATIC_KEY_FALSE_RO(__use_tsc);
> >
> > So sure, we can absolutely do that, but do we want to take this one
> > further perhaps? "notsc" on x86_64 makes no sense what so ever. Lets
> > drag things into this millennium.
> >
>
> Just to make sure I follow: currently, for the static key to be enabled, we
> (mostly) need:
> o X86_FEATURE_TSC is in CPUID
> o determine_cpu_tsc_frequencies()->pit_hpet_ptimer_calibrate_cpu() passes
>
> IIUC all X86_64 systems have a TSC, so the CPUID feature should be a given.
>
> AFAICT pit_hpt_ptimer_calibrate_cpu() relies on having either HPET or the
> ACPI PM timer, the latter should be widely available, though X86_PM_TIMER
> can be disabled via EXPERT - is that a fringe case we don't care about, or
> did I miss something? I don't really know this stuff, and I'm trying to
> write a changelog...
Ah, I was mostly just going by the fact that all of x86_64 have TSC and
disabling it makes no sense.
TSC calibration is always 'fun', but I don't know of a system where its
failure causes us to not use TSC, Thomas?
next prev parent reply other threads:[~2023-12-04 18:21 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-20 10:55 [PATCH 0/5] jump_label: Fix __ro_after_init keys for modules & annotate some keys Valentin Schneider
2023-11-20 10:55 ` [PATCH 1/5] jump_label,module: Don't alloc static_key_mod for __ro_after_init keys Valentin Schneider
2023-11-20 21:38 ` kernel test robot
2023-11-20 22:47 ` kernel test robot
2023-11-20 10:55 ` [PATCH 2/5] context_tracking: Make context_tracking_key __ro_after_init Valentin Schneider
2023-11-20 10:55 ` [PATCH 3/5] x86/kvm: Make kvm_async_pf_enabled __ro_after_init Valentin Schneider
2023-11-27 22:20 ` Sean Christopherson
2023-11-20 10:55 ` [PATCH 4/5] x86/speculation: Make mds_user_clear __ro_after_init Valentin Schneider
2023-11-20 10:55 ` [PATCH 5/5] x86/tsc: Make __use_tsc __ro_after_init Valentin Schneider
2023-11-20 12:05 ` Peter Zijlstra
2023-12-04 16:51 ` Valentin Schneider
2023-12-04 18:20 ` Peter Zijlstra [this message]
2024-01-02 15:09 ` Valentin Schneider
2023-12-02 16:36 ` [PATCH 0/5] jump_label: Fix __ro_after_init keys for modules & annotate some keys Josh Poimboeuf
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