linux-kernel - Re: [PATCH] Enable haltpoll for arm64

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Date:   Wed, 9 Aug 2023 15:48:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mihai Carabas <mihai.carabas@...cle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Petr Mladek <pmladek@...e.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Juerg Haefliger <juerg.haefliger@...onical.com>,
        Mickaël Salaün <mic@...ikod.net>,
        Joao Martins <joao.m.martins@...cle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] Enable haltpoll for arm64

On Wed, Aug 09, 2023 at 02:39:34PM +0300, Mihai Carabas wrote:

> Joao Martins (7):
>   cpuidle-haltpoll: Make boot_option_idle_override check X86 specific
>   x86: Move ARCH_HAS_CPU_RELAX to arch
>   x86/kvm: Move haltpoll_want() to be arch defined
>   governors/haltpoll: Drop kvm_para_available() check
>   arm64: Select ARCH_HAS_CPU_RELAX
>   arm64: Define TIF_POLLING_NRFLAG
>   cpuidle-haltpoll: ARM64 support

You have far too many SOB's on some or all of these patches.

Using poll_state as is on arm64 seems sub-optimal, would not something
like the below make sense?

---
diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index 9b6d90a72601..9ab40198b042 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -27,7 +27,11 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
 		limit = cpuidle_poll_time(drv, dev);
 
 		while (!need_resched()) {
-			cpu_relax();
+
+			smp_cond_load_relaxed(current_thread_info()->flags,
+					      (VAL & TIF_NEED_RESCHED) ||
+					      (loop_count++ >= POLL_IDLE_RELAX_COUNT));
+
 			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
 				continue;