From: Feng Tang <feng.tang@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
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 22:38:04 +0800 [thread overview]
Message-ID: <20210410143804.GB22054@shbuild999.sh.intel.com> (raw)
In-Reply-To: <87y2dq32xc.ffs@nanos.tec.linutronix.de>
Hi Thomas,
On Sat, Apr 10, 2021 at 11:27:11AM +0200, Thomas Gleixner wrote:
> On Tue, Mar 30 2021 at 16:25, Feng Tang wrote:
> > Normally the tsc_sync will be checked every time system enters idle state,
> > but there is still caveat that a system won't enter idle, either because
> > it's too busy or configured purposely to not enter idle. Setup a periodic
> > timer to make sure the check is always on.
>
> Bah. I really hate the fact that we don't have a knob to disable writes
> to the TSC/TSC_ADJUST msrs. That would spare this business alltogether.
>
> > +/*
> > + * Normally the tsc_sync will be checked every time system enters idle state,
> > + * but there is still caveat that a system won't enter idle, either because
> > + * it's too busy or configured purposely to not enter idle.
> > + *
> > + * So setup a periodic timer to make sure the check is always on.
> > + */
> > +
> > +#define SYNC_CHECK_INTERVAL (HZ * 600)
> > +static void tsc_sync_check_timer_fn(struct timer_list *unused)
>
> I've surely mentioned this before that glueing a define without an empty
> newline to a function definition is horrible to read.
Got it, will add a newline.
> > +{
> > + int next_cpu;
> > +
> > + tsc_verify_tsc_adjust(false);
> > +
> > + /* Loop to do the check for all onlined CPUs */
>
> I don't see a loop here.
I meant to loop all onlined CPUs, and the comment could be
changed to
/* Run the check for all onlined CPUs in turn */
> > + next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
>
> Why raw_smp_processor_id()? What's wrong with smp_processor_id()?
Will change to smp_processor_id() for this timer function.
> > + if (next_cpu >= nr_cpu_ids)
> > + next_cpu = cpumask_first(cpu_online_mask);
> > +
> > + tsc_sync_check_timer.expires += SYNC_CHECK_INTERVAL;
> > + add_timer_on(&tsc_sync_check_timer, next_cpu);
> > +}
> > +
> > +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' ?
Thanks,
Feng
>
> Thanks,
>
> tglx
next prev parent reply other threads:[~2021-04-10 14:38 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 [this message]
2021-04-10 18:46 ` Thomas Gleixner
2021-04-11 7:21 ` Feng Tang
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