From: Will Deacon <will@kernel.org>
To: Mihai Carabas <mihai.carabas@oracle.com>
Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
catalin.marinas@arm.com, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, x86@kernel.org, hpa@zytor.com, pbonzini@redhat.com,
wanpengli@tencent.com, vkuznets@redhat.com, rafael@kernel.org,
daniel.lezcano@linaro.org, akpm@linux-foundation.org,
pmladek@suse.com, peterz@infradead.org, dianders@chromium.org,
npiggin@gmail.com, rick.p.edgecombe@intel.com,
joao.m.martins@oracle.com, juerg.haefliger@canonical.com,
mic@digikod.net, arnd@arndb.de, ankur.a.arora@oracle.com
Subject: Re: [PATCH 7/7] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
Date: Mon, 29 Jan 2024 18:15:47 +0000 [thread overview]
Message-ID: <20240129181547.GA12305@willie-the-truck> (raw)
In-Reply-To: <1b3650c5-822e-4789-81d2-0304573cabd9@oracle.com>
On Sun, Jan 28, 2024 at 11:22:50PM +0200, Mihai Carabas wrote:
> La 11.12.2023 13:46, Will Deacon a scris:
> > On Mon, Nov 20, 2023 at 04:01:38PM +0200, Mihai Carabas wrote:
> > > cpu_relax on ARM64 does a simple "yield". Thus we replace it with
> > > smp_cond_load_relaxed which basically does a "wfe".
> > >
> > > Suggested-by: Peter Zijlstra <peterz@infradead.org>
> > > Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
> > > ---
> > > drivers/cpuidle/poll_state.c | 14 +++++++++-----
> > > 1 file changed, 9 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
> > > index 9b6d90a72601..440cd713e39a 100644
> > > --- 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;
> > Doesn't this make ARCH_HAS_CPU_RELAX a complete misnomer?
>
> This controls the build of poll_state.c and the generic definition of
> smp_cond_load_relaxed (used by x86) is using cpu_relax(). Do you propose
> other approach here?
Give it a better name? Having ARCH_HAS_CPU_RELAX control a piece of code
that doesn't use cpu_relax() doesn't make sense to me.
Will
next prev parent reply other threads:[~2024-01-29 18:15 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-20 14:01 [PATCH v2] Enable haltpoll for arm64 Mihai Carabas
2023-11-20 14:01 ` [PATCH 1/7] x86: Move ARCH_HAS_CPU_RELAX to arch Mihai Carabas
2023-11-27 14:44 ` Petr Mladek
2023-11-28 14:09 ` Mihai Carabas
2023-11-20 14:01 ` [PATCH 2/7] x86/kvm: Move haltpoll_want() to be arch defined Mihai Carabas
2023-11-29 20:55 ` Rafael J. Wysocki
2023-11-20 14:01 ` [PATCH 3/7] governors/haltpoll: Drop kvm_para_available() check Mihai Carabas
2023-11-20 14:01 ` [PATCH 4/7] arm64: Select ARCH_HAS_CPU_RELAX Mihai Carabas
2023-11-20 14:01 ` [PATCH 5/7] arm64: Define TIF_POLLING_NRFLAG Mihai Carabas
2023-11-20 14:01 ` [PATCH 6/7] cpuidle-haltpoll: ARM64 support Mihai Carabas
2023-11-20 14:01 ` [PATCH 7/7] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed Mihai Carabas
2023-11-22 20:51 ` Christoph Lameter
2023-11-22 21:33 ` Mihai Carabas
2023-11-27 20:17 ` Christoph Lameter (Ampere)
2023-12-01 6:59 ` Ankur Arora
2023-12-11 11:46 ` Will Deacon
2024-01-28 21:22 ` Mihai Carabas
2024-01-29 18:15 ` Will Deacon [this message]
2024-02-05 12:28 ` Mihai Carabas
2024-02-05 19:33 ` Ankur Arora
2024-01-17 21:19 ` [PATCH v2] Enable haltpoll for arm64 Christoph Lameter (Ampere)
2024-01-25 14:39 ` Mihai Carabas
2024-01-25 15:16 ` Rafael J. Wysocki
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