On 9/20/20 5:39 PM, Marek Behun wrote:
On Sun, 20 Sep 2020 16:15:09 +0200
Jacek Anaszewski <jacek.anaszewski@xxxxxxxxx> wrote:
Hi Pavel,
On 9/19/20 11:38 AM, Pavel Machek wrote:
commit 318681d3e019e39354cc6c2155a7fd1bb8e8084d
Author: Pavel Machek <pavel@xxxxxx>
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@xxxxxx>
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@xxxxxxxxxx>
* Copyright 2011 - 2012 Bryan Wu <bryan.wu@xxxxxxxxxxxxx>
@@ -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
