Messages in this thread | | | Subject | Re: ledtrig-cpu: Limit to 4 CPUs | From | Jacek Anaszewski <> | Date | Tue, 22 Sep 2020 22:41:35 +0200 |
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Hi Pavel,
On 9/22/20 12:42 AM, Pavel Machek wrote: > Hi! > >>> Can I get details of your setup? >> >> I don't use this trigger, but I can imagine that someone does. > > Well, if someone exists, we can increase the limit, or convince them > to change their setup.
Linux is used in many commercial projects and each such change generates a cost, so this is not a sheer matter of convincing someone.
>>> What CPU type that is, and how are you mapping CPU activity to LEDs? >> >> The type of CPU is irrelevant here. What is important is the fact >> that with this trigger it is possible to visually monitor CPU core >> online state. Probably it would be good to ask the author of that >> trigger about his use case. > > It is relevant -- cpu trigger never worked on x86. I had patch fixing > it, but got pushback.
You mean literally x86 (32-bit)? Because I checked yesterday on my x86_64 and it worked just fine, i.e. changing cpu online state generated events on all userspace LEDs I registered for each cpuN trigger.
>> I have spoken up, because I don't get the reason for your patch. >> This driver was reworked year ago to remove PAGE_SIZE limit, >> and I even applied it to my for-next tree, but that was at >> the time of handling maintainership to yourself, and you >> seem to not have picked that commit. >> >> Was that intentional? We had even Greg's ack [0]. > > I checked, and I believe the commit is in:
Indeed, I blindly sought the changeset in git log for ledtrig-cpu.c file.
> #ifdef CONFIG_LEDS_TRIGGERS > static BIN_ATTR(trigger, 0644, led_trigger_read, led_trigger_write, > 0); > static struct bin_attribute *led_trigger_bin_attrs[] = { > > So.. no, it is not causing kernel crashes or something. But it is > example of bad interface, and _that_ is causing problems. (And yes, if > I realized it is simply possible to limit it, maybe the BIN_ATTR > conversion would not be neccessary...)
The limitation you proposed breaks the trigger on many plafforms.
-- Best regards, Jacek Anaszewski
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