linux-kernel - Re: [PATCH 0/6 v3] cpuidle: Handle TIF_NR_POLLING on behalf of polling idle states

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Message-ID: <8278ff79-9acd-4f5a-8525-fb800fac4775@amd.com>
Date: Fri, 17 Jan 2025 23:21:42 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Frederic Weisbecker <frederic@...nel.org>, LKML
	<linux-kernel@...r.kernel.org>
CC: "Rafael J . Wysocki" <rafael@...nel.org>, Daniel Lezcano
	<daniel.lezcano@...aro.org>, <linux-pm@...r.kernel.org>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, Peter Zijlstra
	<peterz@...radead.org>
Subject: Re: [PATCH 0/6 v3] cpuidle: Handle TIF_NR_POLLING on behalf of
 polling idle states

Hello Frederic,

On 1/2/2025 8:31 PM, Frederic Weisbecker wrote:
> The TIF_NR_POLLING handling against TIF_NEED_RESCHED polling/monitoring
> idle states (mwait and also software polling) is a bit messy, with quite
> some wasted cycles spent on useless atomic operations. This tries to
> consolidate this state handling from the cpuidle core.

I tested this series on my 3rd Generation EPYC System with ipistorm and
I've not observed any regressions in IPI throughput to idle CPUs in
TIF_POLLING mode. Additionally tested few microbenchmarks and there were
no surprises there either. Feel free to add:

Tested-by: K Prateek Nayak <kprateek.nayak@....com>

-- 
Thanks and Regards,
Prateek

> 
> Changes since v2:
> 
> _ Handle buggy mwait implementations (thanks Rafael)
> 
> Frederic Weisbecker (4):
>    cpuidle: Remove unnecessary current_clr_polling_and_test() from
>      haltpoll
>    x86/cpuidle: Move buggy mwait implementations away from
>      CPUIDLE_FLAG_MWAIT
>    cpuidle: Remove call_cpuidle_s2idle()
>    cpuidle: Handle TIF_NR_POLLING on behalf of software polling idle
>      states
> 
> Peter Zijlstra (2):
>    cpuidle: Introduce CPUIDLE_FLAG_MWAIT
>    cpuidle: Handle TIF_NR_POLLING on behalf of CPUIDLE_FLAG_MWAIT states
> 
>   arch/arm/include/asm/cpuidle.h     |  2 ++
>   arch/arm64/include/asm/cpuidle.h   |  3 ++
>   arch/powerpc/include/asm/cpuidle.h |  4 +++
>   arch/riscv/include/asm/cpuidle.h   |  2 ++
>   arch/x86/include/asm/cpuidle.h     | 12 +++++++
>   arch/x86/include/asm/mwait.h       | 27 +++++++--------
>   drivers/acpi/processor_idle.c      |  5 +++
>   drivers/cpuidle/cpuidle-haltpoll.c |  3 --
>   drivers/cpuidle/cpuidle-powernv.c  | 10 ------
>   drivers/cpuidle/cpuidle-pseries.c  | 11 -------
>   drivers/cpuidle/cpuidle.c          | 22 ++++++++++++-
>   drivers/cpuidle/poll_state.c       | 30 +++++++----------
>   drivers/idle/intel_idle.c          |  8 +++++
>   include/asm-generic/Kbuild         |  1 +
>   include/asm-generic/cpuidle.h      | 10 ++++++
>   include/linux/cpuidle.h            |  1 +
>   include/linux/sched/idle.h         |  7 +++-
>   kernel/sched/idle.c                | 53 +++++++++---------------------
>   18 files changed, 114 insertions(+), 97 deletions(-)
>   create mode 100644 arch/x86/include/asm/cpuidle.h
>   create mode 100644 include/asm-generic/cpuidle.h
>