From: Quentin Perret <qperret@google.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: rjw@rjwysocki.net, rafael@kernel.org, arnd@arndb.de,
mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org,
mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
vincent.guittot@linaro.org, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
kernel-team@android.com, tkjos@google.com,
adharmap@codeaurora.org
Subject: Re: [PATCH 2/2] cpufreq: Specify default governor on command line
Date: Tue, 16 Jun 2020 10:48:02 +0100 [thread overview]
Message-ID: <20200616094802.GA139416@google.com> (raw)
In-Reply-To: <20200616092759.rjnk3lef4tedfust@vireshk-i7>
On Tuesday 16 Jun 2020 at 14:57:59 (+0530), Viresh Kumar wrote:
> There is another problem here which we need to look at. Any governor
> which is built as a module and isn't currently used, should be allowed
> to unload. And this needs to be tested by you as well, should be easy
> enough.
>
> With the current implementation, you take a reference to the default
> governor when the driver is registered and drop it only when the
> driver goes away. Which means we won't be able to unload the module of
> the governor even if it isn't used. Which is wrong. The solution I
> proposed had the same issue as well.
>
> You need to figure out a way where we don't need to keep holding the
> module hostage even when it isn't used. I see two ways at least for
> the same:
>
> - Do that from the existing place: cpufreq_init_policy().
>
> - And I think this can be done from governor-register/unregister as
> well.
>
> Second one sounds good, if it is feasible to do that.
Good point.
I'm thinking something along the lines of:
---8<---
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 0f05caedc320..a9219404e07f 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2340,6 +2340,11 @@ int cpufreq_register_governor(struct cpufreq_governor *governor)
list_add(&governor->governor_list, &cpufreq_governor_list);
}
+ if (!strncasecmp(cpufreq_param_governor, governor->name, CPUFREQ_NAME_LEN))
+ default_governor = governor;
+ else if (!default_governor && cpufreq_default_governor() == governor)
+ default_governor = cpufreq_default_governor();
+
mutex_unlock(&cpufreq_governor_mutex);
return err;
}
@@ -2368,6 +2373,8 @@ void cpufreq_unregister_governor(struct cpufreq_governor *governor)
mutex_lock(&cpufreq_governor_mutex);
list_del(&governor->governor_list);
+ if (governor == default_governor)
+ default_governor = cpufreq_default_governor();
mutex_unlock(&cpufreq_governor_mutex);
}
EXPORT_SYMBOL_GPL(cpufreq_unregister_governor);
--->8---
should do the trick. That removes the unnecessary reference count, and
feels like a good place to hook things -- that is how cpuidle does it
too IIRC.
I'll double check the locking/synchronization, but that shouldn't be too
bad (famous last words).
Cheers,
Quentin
next prev parent reply other threads:[~2020-06-16 9:48 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-15 16:55 [PATCH 0/2] cpufreq: Specify the default governor on command line Quentin Perret
2020-06-15 16:55 ` [PATCH 1/2] cpufreq: Register governors at core_initcall Quentin Perret
2020-06-16 4:28 ` Viresh Kumar
2020-06-16 8:31 ` Quentin Perret
2020-06-15 16:55 ` [PATCH 2/2] cpufreq: Specify default governor on command line Quentin Perret
2020-06-15 17:41 ` Quentin Perret
2020-06-16 4:31 ` Viresh Kumar
2020-06-16 8:31 ` Quentin Perret
2020-06-16 9:27 ` Viresh Kumar
2020-06-16 9:48 ` Quentin Perret [this message]
2020-06-16 9:54 ` Viresh Kumar
2020-06-16 9:56 ` Quentin Perret
2020-06-22 0:54 ` [cpufreq] d83f959b5e: kmsg.cpufreq:cpufreq_online:Failed_to_initialize_policy_for_cpu:#(-#) kernel test robot
2020-06-23 9:25 ` Quentin Perret
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