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Message-ID: <ceab7277-b95e-477c-9729-d46dc5be54c8@oracle.com>
Date: Mon, 29 Jan 2024 21:20:57 +0200
From: Mihai Carabas <mihai.carabas@...cle.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v3 7/7] cpuidle/poll_state: replace cpu_relax with
smp_cond_load_relaxed
La 29.01.2024 16:52, Rafael J. Wysocki a scris:
> On Mon, Jan 29, 2024 at 12:56 PM Mihai Carabas <mihai.carabas@...cle.com> 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@...radead.org>
>> Signed-off-by: Mihai Carabas <mihai.carabas@...cle.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));
> The inner parens are not necessary AFAICS.
Provides better reading. Do you want to remove these?
> Also, doesn't this return a value which can be used for checking if
> _TIF_NEED_RESCHED is set instead of the condition below?
Yes, indeed - should I modify this check? (somehow I wanted to preserve
the original check)
Thank you,
Mihai
>> +
>> + 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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