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From: Thomas Gleixner <tglx@linutronix.de>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: linux-kernel@vger.kernel.org,
	Daniel Bristot de Oliveira <bristot@kernel.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Valentin Schneider <vschneid@redhat.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Leonardo Bras <leobras@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [patch 05/12] timekeeping_notify: use stop_machine_fail when appropriate
Date: Thu, 08 Feb 2024 16:23:58 +0100	[thread overview]
Message-ID: <87zfwbkmi9.ffs@tglx> (raw)
In-Reply-To: <ZcN+XM4223HS42LM@tpad>

On Wed, Feb 07 2024 at 09:58, Marcelo Tosatti wrote:
> On Wed, Feb 07, 2024 at 12:57:19PM +0100, Thomas Gleixner wrote:
>> On Tue, Feb 06 2024 at 15:49, Marcelo Tosatti wrote:
>> > Change timekeeping_notify to use stop_machine_fail when appropriate,
>> > which will fail in case the target CPU is tagged as block interference
>> > CPU.
>> 
>> You completely fail to explain 'appropriate'. There is zero reason for
>> this churn, really.
>
> The churn is so that we can return an error to
> current_clocksource_store (sysfs handler for writes to
> /sys/devices/system/clocksource/clocksource0/current_clocksource).

What for? Why?

Writing to that file requires root. Root can rightfully screw up a
system and adding a debugfs based "prevention" mechanism is not making
this any better because root can just clear the CPU mask there and move
on.

So what is the actual real world problem solved by these patches?

All I've seen so far is handwaving about interference prevention and TBH
I can't squint hard enough to believe that.

Thanks,

        tglx

  reply	other threads:[~2024-02-08 15:23 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-06 18:49 [patch 00/12] cpu isolation: infra to block interference to select CPUs Marcelo Tosatti
2024-02-06 18:49 ` [patch 01/12] cpu isolation: basic block interference infrastructure Marcelo Tosatti
2024-02-06 18:49 ` [patch 02/12] introduce smp_call_func_single_fail Marcelo Tosatti
2024-02-06 18:49 ` [patch 03/12] Introduce _fail variants of stop_machine functions Marcelo Tosatti
2024-02-06 18:49 ` [patch 04/12] clockevent unbind: use smp_call_func_single_fail Marcelo Tosatti
2024-02-07 11:55   ` Thomas Gleixner
2024-02-07 12:51     ` Marcelo Tosatti
2024-02-11  8:52       ` Thomas Gleixner
2024-02-14 18:58         ` Marcelo Tosatti
2024-02-06 18:49 ` [patch 05/12] timekeeping_notify: use stop_machine_fail when appropriate Marcelo Tosatti
2024-02-07 11:57   ` Thomas Gleixner
2024-02-07 12:58     ` Marcelo Tosatti
2024-02-08 15:23       ` Thomas Gleixner [this message]
2024-02-09 15:30         ` Marcelo Tosatti
2024-02-12 15:29           ` Thomas Gleixner
2024-02-06 18:49 ` [patch 06/12] perf_event_open: check for block interference CPUs Marcelo Tosatti
2024-02-06 18:49 ` [patch 07/12] mtrr_add_page/mtrr_del_page: " Marcelo Tosatti
2024-02-06 18:49 ` [patch 08/12] arm64 kernel/topology: use smp_call_function_single_fail Marcelo Tosatti
2024-02-06 18:49 ` [patch 09/12] AMD MCE: use smp_call_func_single_fail Marcelo Tosatti
2024-02-06 18:49 ` [patch 10/12] x86/mce/inject.c: fail if target cpu is block interference Marcelo Tosatti
2024-02-06 18:49 ` [patch 11/12] x86/resctrl: use smp_call_function_single_fail Marcelo Tosatti
2024-02-12 15:19   ` Thomas Gleixner
2024-02-14 18:59     ` Marcelo Tosatti
2024-02-06 18:49 ` [patch 12/12] x86/cacheinfo.c: check for block interference CPUs Marcelo Tosatti
2024-02-07 12:41   ` Thomas Gleixner
2024-02-07 13:10     ` Marcelo Tosatti
2024-02-07 13:16       ` Marcelo Tosatti

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