Messages in this thread | | | Subject | Re: ledtrig-cpu: Limit to 4 CPUs | From | Jacek Anaszewski <> | Date | Sun, 20 Sep 2020 18:55:28 +0200 |
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On 9/20/20 5:39 PM, Marek Behun wrote: > 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?
I have an access to the machine with 80 cpus, so I could once get surprised not being able to find cpuN triggers not being listed among available triggers.
And say that I have a solution where I install 80 userspace LEDs (drivers/leds/uleds.c) and register them on each cpuN triggers to get notifications on how cpus work.
> 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.
Yes, we can do that, and even mark the cpu trigger as legacy but we cannot prevent people from using it if that was present in kernel for many years.
-- Best regards, Jacek Anaszewski
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