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From: Valentin Schneider <vschneid@redhat.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, kvm@vger.kernel.org,
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Subject: Re: [RFC PATCH v2 15/20] context-tracking: Introduce work deferral infrastructure
Date: Tue, 25 Jul 2023 14:05:47 +0100	[thread overview]
Message-ID: <xhsmhwmyorvis.mognet@vschneid.remote.csb> (raw)
In-Reply-To: <ZL+wgn76H1em9hZU@lothringen>

On 25/07/23 13:22, Frederic Weisbecker wrote:
> On Tue, Jul 25, 2023 at 11:10:31AM +0100, Valentin Schneider wrote:
>> I have reasons! I just swept them under the rug and didn't mention them :D
>> Also looking at the config dependencies again I got it wrong, but
>> nevertheless that means I get to ramble about it.
>>
>> With NO_HZ_IDLE, we get CONTEXT_TRACKING_IDLE, so we get these
>> transitions:
>>
>>   ct_idle_enter()
>>     ct_kernel_exit()
>>       ct_state_inc_clear_work()
>>
>>   ct_idle_exit()
>>     ct_kernel_enter()
>>       ct_work_flush()
>>
>> Now, if we just make CONTEXT_TRACKING_WORK depend on CONTEXT_TRACKING_IDLE
>> rather than CONTEXT_TRACKING_USER, we get to leverage the IPI deferral for
>> NO_HZ_IDLE kernels - in other words, we get to keep idle CPUs idle longer.
>>
>> It's a completely different argument than reducing interference for
>> NOHZ_FULL userspace applications and I should have at the very least
>> mentioned it in the cover letter, but it's the exact same backing
>> mechanism.
>>
>> Looking at it again, I'll probably make the CONTEXT_IDLE thing a separate
>> patch with a proper changelog.
>
> Ok should that be a seperate Kconfig? This indeed can bring power improvement
> but at the cost of more overhead from the sender. A balance to be measured...

Yep agreed, I'll make that an optional config.



  reply	other threads:[~2023-07-25 13:07 UTC|newest]

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-20 16:30 [RFC PATCH v2 00/20] context_tracking,x86: Defer some IPIs until a user->kernel transition Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 01/20] tracing/filters: Dynamically allocate filter_pred.regex Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 02/20] tracing/filters: Enable filtering a cpumask field by another cpumask Valentin Schneider
2023-07-26 19:41   ` Josh Poimboeuf
2023-07-27  9:46     ` Valentin Schneider
2023-07-29 19:09     ` Steven Rostedt
2023-07-31 11:19       ` Valentin Schneider
2023-07-31 15:48         ` Steven Rostedt
2023-07-20 16:30 ` [RFC PATCH v2 03/20] tracing/filters: Enable filtering a scalar field by a cpumask Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 04/20] tracing/filters: Enable filtering the CPU common " Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 05/20] tracing/filters: Optimise cpumask vs cpumask filtering when user mask is a single CPU Valentin Schneider
2023-07-29 19:34   ` Steven Rostedt
2023-07-31 11:20     ` Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 06/20] tracing/filters: Optimise scalar vs cpumask filtering when the " Valentin Schneider
2023-07-29 19:55   ` Steven Rostedt
2023-07-31 11:20     ` Valentin Schneider
2023-07-31 12:07     ` Dan Carpenter
2023-07-31 15:54       ` Steven Rostedt
2023-07-31 16:03         ` Dan Carpenter
2023-07-31 17:20           ` Valentin Schneider
2023-07-31 18:16           ` Steven Rostedt
2023-07-20 16:30 ` [RFC PATCH v2 07/20] tracing/filters: Optimise CPU " Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 08/20] tracing/filters: Further optimise scalar vs cpumask comparison Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 09/20] tracing/filters: Document cpumask filtering Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 10/20] jump_label,module: Don't alloc static_key_mod for __ro_after_init keys Valentin Schneider
2023-07-28 22:04   ` Peter Zijlstra
2023-07-20 16:30 ` [RFC PATCH v2 11/20] objtool: Flesh out warning related to pv_ops[] calls Valentin Schneider
2023-07-28 15:33   ` Josh Poimboeuf
2023-07-31 11:16     ` Valentin Schneider
2023-07-31 21:36       ` Josh Poimboeuf
2023-07-31 21:46         ` Peter Zijlstra
2023-08-01 16:06           ` Josh Poimboeuf
2023-08-01 18:12             ` Peter Zijlstra
2023-07-20 16:30 ` [RFC PATCH v2 12/20] objtool: Warn about non __ro_after_init static key usage in .noinstr Valentin Schneider
2023-07-28 15:35   ` Josh Poimboeuf
2023-07-31 11:18     ` Valentin Schneider
2023-07-28 16:02   ` Josh Poimboeuf
2023-07-31 11:18     ` Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 13/20] context_tracking: Make context_tracking_key __ro_after_init Valentin Schneider
2023-07-28 16:00   ` Josh Poimboeuf
2023-07-31 11:16     ` Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 14/20] x86/kvm: Make kvm_async_pf_enabled __ro_after_init Valentin Schneider
2023-10-09 16:40   ` Maxim Levitsky
2023-07-20 16:30 ` [RFC PATCH v2 15/20] context-tracking: Introduce work deferral infrastructure Valentin Schneider
2023-07-24 14:52   ` Frederic Weisbecker
2023-07-24 16:55     ` Valentin Schneider
2023-07-24 19:18       ` Frederic Weisbecker
2023-07-25 10:10         ` Valentin Schneider
2023-07-25 11:22           ` Frederic Weisbecker
2023-07-25 13:05             ` Valentin Schneider [this message]
2023-07-20 16:30 ` [RFC PATCH v2 16/20] rcu: Make RCU dynticks counter size configurable Valentin Schneider
2023-07-21  8:17   ` Valentin Schneider
2023-07-21 14:10     ` Paul E. McKenney
2023-07-21 15:08       ` Valentin Schneider
2023-07-21 16:09         ` Paul E. McKenney
2023-07-20 16:30 ` [RFC PATCH v2 17/20] rcutorture: Add a test config to torture test low RCU_DYNTICKS width Valentin Schneider
2023-07-20 19:53   ` Paul E. McKenney
2023-07-21  4:00     ` Paul E. McKenney
2023-07-21  7:58       ` Valentin Schneider
2023-07-21 14:07         ` Paul E. McKenney
2023-07-21 15:08           ` Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 18/20] context_tracking,x86: Defer kernel text patching IPIs Valentin Schneider
2023-07-25 10:49   ` Joel Fernandes
2023-07-25 13:36     ` Valentin Schneider
2023-07-25 17:41       ` Joel Fernandes
2023-07-25 13:39     ` Peter Zijlstra
2023-07-25 17:47       ` Joel Fernandes
2023-07-20 16:30 ` [RFC PATCH v2 19/20] context_tracking,x86: Add infrastructure to defer kernel TLBI Valentin Schneider
2023-07-20 16:30 ` [RFC PATCH v2 20/20] x86/mm, mm/vmalloc: Defer flush_tlb_kernel_range() targeting NOHZ_FULL CPUs Valentin Schneider
2023-07-21 18:15   ` Nadav Amit
2023-07-24 11:32     ` Valentin Schneider
2023-07-24 17:40       ` Dave Hansen
2023-07-25 13:21         ` Peter Zijlstra
2023-07-25 14:03           ` Valentin Schneider
2023-07-25 16:37         ` Marcelo Tosatti
2023-07-25 17:12           ` Dave Hansen

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