From: Mihai Carabas <mihai.carabas@oracle.com>
To: Will Deacon <will@kernel.org>
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, 5 Feb 2024 14:28:13 +0200 [thread overview]
Message-ID: <1b25b492-b9e7-4411-90d1-463d44084043@oracle.com> (raw)
In-Reply-To: <20240129181547.GA12305@willie-the-truck>
>>>> 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.
The generic code for smp_cond_load_relaxed is using cpu_relax and this
one is used on x86 - so ARCH_HAS_CPU_RELAX is a prerequisite on x86 when
using haltpoll. Only on ARM64 this is overwritten. Moreover
ARCH_HAS_CPU_RELAX is controlling the function definition for
cpuidle_poll_state_init (this is how it was originally designed).
Thanks,
Mihai
next prev parent reply other threads:[~2024-02-05 12:29 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
2024-02-05 12:28 ` Mihai Carabas [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1b25b492-b9e7-4411-90d1-463d44084043@oracle.com \
--to=mihai.carabas@oracle.com \
--cc=akpm@linux-foundation.org \
--cc=ankur.a.arora@oracle.com \
--cc=arnd@arndb.de \
--cc=bp@alien8.de \
--cc=catalin.marinas@arm.com \
--cc=daniel.lezcano@linaro.org \
--cc=dianders@chromium.org \
--cc=hpa@zytor.com \
--cc=joao.m.martins@oracle.com \
--cc=juerg.haefliger@canonical.com \
--cc=kvm@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=mic@digikod.net \
--cc=mingo@redhat.com \
--cc=npiggin@gmail.com \
--cc=pbonzini@redhat.com \
--cc=peterz@infradead.org \
--cc=pmladek@suse.com \
--cc=rafael@kernel.org \
--cc=rick.p.edgecombe@intel.com \
--cc=tglx@linutronix.de \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
--cc=will@kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).