From: Marek Behun <marek.behun@nic.cz>
To: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>,
linux-leds@vger.kernel.org, dmurphy@ti.com,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: ledtrig-cpu: Limit to 4 CPUs
Date: Sun, 20 Sep 2020 17:39:05 +0200 [thread overview]
Message-ID: <20200920173905.237c314e@nic.cz> (raw)
In-Reply-To: <27e19ac9-4bc0-2945-3985-6cd6bb5407df@gmail.com>
On Sun, 20 Sep 2020 16:15:09 +0200
Jacek Anaszewski <jacek.anaszewski@gmail.com> wrote:
> Hi Pavel,
>
> On 9/19/20 11:38 AM, Pavel Machek wrote:
> > commit 318681d3e019e39354cc6c2155a7fd1bb8e8084d
> > Author: Pavel Machek <pavel@ucw.cz>
> > Date: Sat Sep 19 11:34:58 2020 +0200
> >
> > ledtrig-cpu: Limit to 4 CPUs
> >
> > Some machines have thousands of CPUs... and trigger mechanisms was not
> > really meant for thousands of triggers. I doubt anyone uses this
> > trigger on many-CPU machine; but if they do, they'll need to do it
> > properly.
> >
> > Signed-off-by: Pavel Machek <pavel@ucw.cz>
> >
> > diff --git a/drivers/leds/trigger/ledtrig-cpu.c b/drivers/leds/trigger/ledtrig-cpu.c
> > index 869976d1b734..b7e00b09b137 100644
> > --- a/drivers/leds/trigger/ledtrig-cpu.c
> > +++ b/drivers/leds/trigger/ledtrig-cpu.c
> > @@ -2,14 +2,18 @@
> > /*
> > * ledtrig-cpu.c - LED trigger based on CPU activity
> > *
> > - * This LED trigger will be registered for each possible CPU and named as
> > - * cpu0, cpu1, cpu2, cpu3, etc.
> > + * This LED trigger will be registered for first four CPUs and named
> > + * as cpu0, cpu1, cpu2, cpu3. There's additional trigger called cpu that
> > + * is on when any CPU is active.
> > + *
> > + * If you want support for arbitrary number of CPUs, make it one trigger,
> > + * with additional sysfs file selecting which CPU to watch.
> > *
> > * It can be bound to any LED just like other triggers using either a
> > * board file or via sysfs interface.
> > *
> > * An API named ledtrig_cpu is exported for any user, who want to add CPU
> > - * activity indication in their code
> > + * activity indication in their code.
> > *
> > * Copyright 2011 Linus Walleij <linus.walleij@linaro.org>
> > * Copyright 2011 - 2012 Bryan Wu <bryan.wu@canonical.com>
> > @@ -145,6 +149,9 @@ static int __init ledtrig_cpu_init(void)
> > for_each_possible_cpu(cpu) {
> > struct led_trigger_cpu *trig = &per_cpu(cpu_trig, cpu);
> >
> > + if (cpu > 4)
>
> NACK. The workaround for this trigger was implemented for a reason -
> to make it working on platforms with arbitrary number of logical cpus.
> I've got 8, so I am discriminated now. Not saying, that it precludes
> trigger registration with no single line of warning.
> Regardless of that - you have no guarantee that you're not breaking
> anyone - "I doubt" is not a sufficient argument.
>
If that is the case Jacek, I would try 16 and then see if people
complain. Do you really think that someone sets a specific LED to
trigger on activity on CPU id > 16?
If you do not agree, then I think we should implement a "cpu" trigger
where the cpu ID (or maybe mask of multiple CPUs) is configurable via
another sysfs file. And then declare current cpu trigger (with names
"cpu%d") as legacy.
Marek
next prev parent reply other threads:[~2020-09-20 15:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200919093833.GA14326@duo.ucw.cz>
2020-09-20 14:15 ` ledtrig-cpu: Limit to 4 CPUs Jacek Anaszewski
2020-09-20 15:39 ` Marek Behun [this message]
2020-09-20 16:55 ` Jacek Anaszewski
2020-09-20 17:33 ` Marek Behun
2020-09-20 17:49 ` Jacek Anaszewski
2020-09-20 18:34 ` Pavel Machek
2020-09-21 22:14 ` Jacek Anaszewski
2020-09-21 22:42 ` Pavel Machek
2020-09-22 20:41 ` Jacek Anaszewski
2020-09-25 8:51 ` Jacek Anaszewski
2020-09-25 9:40 ` Pavel Machek
2020-09-26 13:59 ` Jacek Anaszewski
2020-10-08 10:10 ` Pavel Machek
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