Messages in this thread | | | Subject | Re: ledtrig-cpu: Limit to 4 CPUs | From | Jacek Anaszewski <> | Date | Sun, 20 Sep 2020 19:49:52 +0200 |
| |
On 9/20/20 7:33 PM, Marek Behun wrote: > On Sun, 20 Sep 2020 18:55:28 +0200 > Jacek Anaszewski <jacek.anaszewski@gmail.com> wrote: > >> 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. > > Hi Jacek, > > I understand (and Pavel does for sure too) that many people > currently have that possibility, that they have access to machines with > many CPUs and many LEDs. We also understand that currently it is > possible for users to set 1847th LED to trigger on activity on CPU ID > 1337. What we are suggesting is that practically no one uses this, and > for those 10 people who do, well it would be better for them to migrate > to new ABI than for kernel developers having forever maintain this > legacy ABI. > > Legacy drivers get removed from kernel from time to time, if no one > uses them. So I think Pavel's proposal (although I may not agree with > the limit 4) has some merit. If we try this, and someone complains, we > can then discuss. If we don't try, we may never know.
Just go ahead without my ack. I just wanted not to let it go without any discussion. At least we leave a trace...
>>> 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
| |