From: Thomas Gleixner <tglx@linutronix.de>
To: Feng Tang <feng.tang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H . Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, linux-kernel@vger.kernel.org,
rui.zhang@intel.com, andi.kleen@intel.com, dave.hansen@intel.com,
len.brown@intel.com
Subject: Re: [RFC 1/2] x86/tsc: add a timer to make sure tsc_adjust is always checked
Date: Sat, 10 Apr 2021 20:46:38 +0200 [thread overview]
Message-ID: <87blam2d0x.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210410143804.GB22054@shbuild999.sh.intel.com>
Feng,
On Sat, Apr 10 2021 at 22:38, Feng Tang wrote:
> On Sat, Apr 10, 2021 at 11:27:11AM +0200, Thomas Gleixner wrote:
>> > +static int __init start_sync_check_timer(void)
>> > +{
>> > + if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
>> > + return 0;
>> > +
>> > + timer_setup(&tsc_sync_check_timer, tsc_sync_check_timer_fn, 0);
>> > + tsc_sync_check_timer.expires = jiffies + SYNC_CHECK_INTERVAL;
>> > + add_timer(&tsc_sync_check_timer);
>> > +
>> > + return 0;
>> > +}
>> > +late_initcall(start_sync_check_timer);
>>
>> So right now, if someone adds 'tsc=reliable' on the kernel command line
>> then all of the watchdog checking, except for the idle enter TSC_ADJUST
>> check is disabled. The NOHZ full people are probably going to be pretty
>> unhappy about yet another unconditional timer they have to chase down.
>>
>> So this needs some more thought.
>
> 'tsc=reliable' in cmdline will set 'tsc_clocksource_reliable' to 1, so
> we can skip starting this timer if 'tsc_clocksource_reliable==1' ?
Then we can just ignore that patch alltogether because of 2/2 doing:
+ if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
+ boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
+ boot_cpu_has(X86_FEATURE_TSC_ADJUST) &&
+ nr_online_nodes <= 2)
+ tsc_clocksource_reliable = 1;
....
I said for a reason:
>> So this needs some more thought.
Thanks,
tglx
next prev parent reply other threads:[~2021-04-10 18:46 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-30 8:25 [RFC 1/2] x86/tsc: add a timer to make sure tsc_adjust is always checked Feng Tang
2021-03-30 8:25 ` [RFC 2/2] x86/tsc: mark tsc reliable for qualified platforms Feng Tang
2021-04-10 9:27 ` [RFC 1/2] x86/tsc: add a timer to make sure tsc_adjust is always checked Thomas Gleixner
2021-04-10 9:47 ` Borislav Petkov
2021-04-10 12:11 ` [PATCH] x86/msr: Block writes to certain MSRs unconditionally Borislav Petkov
2021-04-10 14:51 ` Andy Lutomirski
2021-04-10 15:33 ` [PATCH -v1.1] " Borislav Petkov
2021-04-10 18:52 ` [PATCH] " Andi Kleen
2021-04-11 9:40 ` Borislav Petkov
2021-04-11 16:03 ` Andy Lutomirski
2021-04-11 16:43 ` Andi Kleen
2021-04-11 16:57 ` Andy Lutomirski
2021-04-11 17:03 ` Borislav Petkov
2021-04-11 23:21 ` Andy Lutomirski
2021-04-12 9:37 ` Borislav Petkov
2021-04-10 14:48 ` [RFC 1/2] x86/tsc: add a timer to make sure tsc_adjust is always checked Feng Tang
2021-04-10 15:38 ` Borislav Petkov
2021-04-10 18:43 ` Thomas Gleixner
2021-04-10 14:38 ` Feng Tang
2021-04-10 18:46 ` Thomas Gleixner [this message]
2021-04-11 7:21 ` Feng Tang
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