From: Mihai Carabas <mihai.carabas@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
"Will Deacon" <will@kernel.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Wanpeng Li" <wanpengli@tencent.com>,
"Vitaly Kuznetsov" <vkuznets@redhat.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
"Daniel Lezcano" <daniel.lezcano@linaro.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Kees Cook" <keescook@chromium.org>,
"Petr Mladek" <pmladek@suse.com>,
"Ard Biesheuvel" <ardb@kernel.org>,
"Sami Tolvanen" <samitolvanen@google.com>,
"Nicholas Piggin" <npiggin@gmail.com>,
"Juerg Haefliger" <juerg.haefliger@canonical.com>,
"Mickaël Salaün" <mic@digikod.net>,
"Joao Martins" <joao.m.martins@oracle.com>,
"Arnd Bergmann" <arnd@arndb.de>,
"Ankur Arora" <ankur.a.arora@oracle.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
linux-pm@vger.kernel.org
Subject: Re: [PATCH] Enable haltpoll for arm64
Date: Tue, 29 Aug 2023 17:31:27 +0300 [thread overview]
Message-ID: <ad2e6b6a-57a3-2c22-8ec8-7ba12e09dbeb@oracle.com> (raw)
In-Reply-To: <20230809134837.GM212435@hirez.programming.kicks-ass.net>
> 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;
>
Thank you for the suggestion. I have tried it and also different
variations like [1] to respect the initial logic
but I obtain poor performance compared to the initial one:
perf bench sched pipe
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes
Total time: 136.215 [sec]
136.215229 usecs/op
7341 ops/sec
[1]
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -26,12 +26,16 @@ static int __cpuidle poll_idle(struct cpuidle_device
*dev,
limit = cpuidle_poll_time(drv, dev);
- while (!need_resched()) {
- cpu_relax();
- if (loop_count++ < POLL_IDLE_RELAX_COUNT)
- continue;
-
+ for (;;) {
loop_count = 0;
+
+ smp_cond_load_relaxed(¤t_thread_info()->flags,
+ (VAL & TIF_NEED_RESCHED) ||
+ (loop_count++ >=
POLL_IDLE_RELAX_COUNT));
+
+ if (loop_count < POLL_IDLE_RELAX_COUNT)
+ break;
+
if (local_clock_noinstr() - time_start > limit) {
dev->poll_time_limit = true;
break;
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prev parent reply other threads:[~2023-08-29 14:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-09 11:39 [PATCH] Enable haltpoll for arm64 Mihai Carabas
2023-08-09 11:39 ` [PATCH 1/7] cpuidle-haltpoll: Make boot_option_idle_override check X86 specific Mihai Carabas
2023-08-10 19:22 ` Rafael J. Wysocki
2023-08-09 11:39 ` [PATCH 2/7] x86: Move ARCH_HAS_CPU_RELAX to arch Mihai Carabas
2023-08-09 11:39 ` [PATCH 3/7] x86/kvm: Move haltpoll_want() to be arch defined Mihai Carabas
2023-08-09 11:39 ` [PATCH 4/7] governors/haltpoll: Drop kvm_para_available() check Mihai Carabas
2023-08-10 19:25 ` Rafael J. Wysocki
2023-08-09 11:39 ` [PATCH 5/7] arm64: Select ARCH_HAS_CPU_RELAX Mihai Carabas
2023-08-09 13:49 ` Peter Zijlstra
2023-08-29 14:49 ` Russell King (Oracle)
2023-08-09 11:39 ` [PATCH 6/7] arm64: Define TIF_POLLING_NRFLAG Mihai Carabas
2023-08-09 11:39 ` [PATCH 7/7] cpuidle-haltpoll: ARM64 support Mihai Carabas
2023-08-09 13:48 ` [PATCH] Enable haltpoll for arm64 Peter Zijlstra
2023-08-29 14:31 ` Mihai Carabas [this message]
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