From: Dmitry Osipenko <digetx@gmail.com>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: "Thierry Reding" <thierry.reding@gmail.com>,
"Jonathan Hunter" <jonathanh@nvidia.com>,
"Peter De Schrijver" <pdeschrijver@nvidia.com>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
"Michał Mirosław" <mirq-linux@rere.qmqm.pl>,
"Jasper Korten" <jja2000@gmail.com>,
"David Heidelberg" <david@ixit.cz>,
"Peter Geis" <pgwipeout@gmail.com>,
linux-pm@vger.kernel.org, linux-tegra@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v9 09/17] arm: tegra20: cpuidle: Handle case where secondary CPU hangs on entering LP2
Date: Fri, 21 Feb 2020 23:54:03 +0300 [thread overview]
Message-ID: <c13aa8f9-092b-55ca-742e-17db0184649b@gmail.com> (raw)
In-Reply-To: <21e3cc35-cc6b-5452-da93-bdaac43716c5@linaro.org>
21.02.2020 23:48, Daniel Lezcano пишет:
> On 21/02/2020 21:21, Dmitry Osipenko wrote:
>> 21.02.2020 23:02, Daniel Lezcano пишет:
>
> [ ... ]
>
>>>>>>>> +
>>>>>>>> + /*
>>>>>>>> + * The primary CPU0 core shall wait for the secondaries
>>>>>>>> + * shutdown in order to power-off CPU's cluster safely.
>>>>>>>> + * The timeout value depends on the current CPU frequency,
>>>>>>>> + * it takes about 40-150us in average and over 1000us in
>>>>>>>> + * a worst case scenario.
>>>>>>>> + */
>>>>>>>> + do {
>>>>>>>> + if (tegra_cpu_rail_off_ready())
>>>>>>>> + return 0;
>>>>>>>> +
>>>>>>>> + } while (ktime_before(ktime_get(), timeout));
>>>>>>>
>>>>>>> So this loop will aggresively call tegra_cpu_rail_off_ready() and retry 3
>>>>>>> times. The tegra_cpu_rail_off_ready() function can be called thoushand of times
>>>>>>> here but the function will hang 1.5s :/
>>>>>>>
>>>>>>> I suggest something like:
>>>>>>>
>>>>>>> while (retries--i && !tegra_cpu_rail_off_ready())
>>>>>>> udelay(100);
>>>>>>>
>>>>>>> So <retries> calls to tegra_cpu_rail_off_ready() and 100us x <retries> maximum
>>>>>>> impact.
>>>>>> But udelay() also results into CPU spinning in a busy-loop, and thus,
>>>>>> what's the difference?
>>>>>
>>>>> busy looping instead of register reads with all the hardware things involved behind.
>>>>
>>>> Please notice that this code runs only on an older Cortex-A9/A15, which
>>>> doesn't support WFE for the delaying, and thus, CPU always busy-loops
>>>> inside udelay().
>>>>
>>>> What about if I'll add cpu_relax() to the loop? Do you think it it could
>>>> have any positive effect?
>>>
>>> I think udelay() has a call to cpu_relax().
>>
>> Yes, my point is that udelay() doesn't bring much benefit for us here
>> because:
>>
>> 1. we want to enter into power-gated state as quick as possible and
>> udelay() just adds an unnecessary delay
>>
>> 2. udelay() spins in a busy-loop until delay is expired, just like we're
>> doing it in this function already
>
> In this case why not remove ktime_get() and increase the number of retries?
Because the busy-loop performance depends on CPU's frequency, so we
can't rely on a bare number of the retries.
next prev parent reply other threads:[~2020-02-21 20:54 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-12 23:51 [PATCH v9 00/17] Consolidate and improve NVIDIA Tegra CPUIDLE driver(s) Dmitry Osipenko
2020-02-12 23:51 ` [PATCH v9 01/17] ARM: tegra: Compile sleep-tegra20/30.S unconditionally Dmitry Osipenko
2020-02-12 23:51 ` [PATCH v9 02/17] ARM: tegra: Add tegra_pm_park_secondary_cpu() Dmitry Osipenko
2020-02-12 23:51 ` [PATCH v9 03/17] ARM: tegra: Remove pen-locking from cpuidle-tegra20 Dmitry Osipenko
2020-02-21 14:58 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 04/17] ARM: tegra: Change tegra_set_cpu_in_lp2() type to void Dmitry Osipenko
2020-02-21 15:04 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 05/17] ARM: tegra: Propagate error from tegra_idle_lp2_last() Dmitry Osipenko
2020-02-21 15:16 ` Daniel Lezcano
2020-02-21 17:21 ` Dmitry Osipenko
2020-02-21 17:40 ` Daniel Lezcano
2020-02-21 18:42 ` Dmitry Osipenko
2020-02-21 19:16 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 06/17] ARM: tegra: Expose PM functions required for new cpuidle driver Dmitry Osipenko
2020-02-21 15:18 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 07/17] ARM: tegra: Rename some of the newly exposed PM functions Dmitry Osipenko
2020-02-21 15:19 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 08/17] ARM: tegra: Make outer_disable() open-coded Dmitry Osipenko
2020-02-12 23:51 ` [PATCH v9 09/17] arm: tegra20: cpuidle: Handle case where secondary CPU hangs on entering LP2 Dmitry Osipenko
2020-02-21 14:55 ` Daniel Lezcano
2020-02-21 15:43 ` Daniel Lezcano
2020-02-21 16:56 ` Dmitry Osipenko
2020-02-21 17:36 ` Daniel Lezcano
2020-02-21 18:19 ` Dmitry Osipenko
2020-02-21 20:02 ` Daniel Lezcano
2020-02-21 20:21 ` Dmitry Osipenko
2020-02-21 20:42 ` Dmitry Osipenko
2020-02-21 20:48 ` Daniel Lezcano
2020-02-21 20:54 ` Dmitry Osipenko [this message]
2020-02-21 21:11 ` Daniel Lezcano
2020-02-24 15:12 ` Dmitry Osipenko
2020-02-12 23:51 ` [PATCH v9 10/17] arm: tegra20: cpuidle: Make abort_flag atomic Dmitry Osipenko
2020-02-21 15:25 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 11/17] arm: tegra20/30: cpuidle: Remove unnecessary memory barrier Dmitry Osipenko
2020-02-21 15:25 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 12/17] cpuidle: Refactor and move out NVIDIA Tegra20 driver into drivers/cpuidle Dmitry Osipenko
2020-02-21 15:44 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 13/17] cpuidle: tegra: Squash Tegra30 driver into the common driver Dmitry Osipenko
2020-02-21 16:29 ` Daniel Lezcano
2020-02-21 16:59 ` Dmitry Osipenko
2020-02-21 17:41 ` Daniel Lezcano
2020-02-21 18:20 ` Dmitry Osipenko
2020-02-12 23:51 ` [PATCH v9 14/17] cpuidle: tegra: Squash Tegra114 " Dmitry Osipenko
2020-02-12 23:51 ` [PATCH v9 15/17] cpuidle: tegra: Disable CC6 state if LP2 unavailable Dmitry Osipenko
2020-02-21 16:39 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 16/17] ARM: multi_v7_defconfig: Enable Tegra cpuidle driver Dmitry Osipenko
2020-02-21 16:30 ` Daniel Lezcano
2020-02-12 23:51 ` [PATCH v9 17/17] ARM: tegra: Enable Tegra cpuidle driver in tegra_defconfig Dmitry Osipenko
2020-02-21 16:31 ` Daniel Lezcano
2020-02-13 0:38 ` [PATCH v9 00/17] Consolidate and improve NVIDIA Tegra CPUIDLE driver(s) Dmitry Osipenko
2020-02-18 14:56 ` Dmitry Osipenko
2020-02-24 16:44 ` Dmitry Osipenko
-- strict thread matches above, loose matches on Subject: below --
2019-12-18 21:04 Dmitry Osipenko
2019-12-18 21:04 ` [PATCH v9 09/17] arm: tegra20: cpuidle: Handle case where secondary CPU hangs on entering LP2 Dmitry Osipenko
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