Re: [PATCH v4 4/5] block: introduce LED block device activity trigger

[Jacek Anaszewski <jacek.anaszewski@gmail.com>]

On 8/19/19 4:38 PM, Pavel Machek wrote:
> On Sat 2019-08-17 22:07:43, Jacek Anaszewski wrote:
>> On 8/17/19 4:55 PM, Pavel Machek wrote:
>>> On Fri 2019-08-16 01:59:58, Akinobu Mita wrote:
>>>> This allows LEDs to be controlled by block device activity.
>>>>
>>>> We already have ledtrig-disk (LED disk activity trigger), but the lower
>>>> level disk drivers need to utilize ledtrig_disk_activity() to make the
>>>> LED blink.
>>>>
>>>> The LED block device trigger doesn't require the lower level drivers to
>>>> have any instrumentation. The activity is collected by polling the disk
>>>> stats.
>>>>
>>>> Example:
>>>>
>>>> echo block-nvme0n1 > /sys/class/leds/diy/trigger
>>>
>>> Lets use one trigger "block" and have the device as a parameter,
>>> please.
>>>
>>> We already have 1000 cpu triggers on 1000 cpu machines, and yes, its a
>>> disaster we'll need to fix. Lets not repeat the same mistake here.
>>>
>>> I guess it may be slightly more work. Sorry about that.
>>
>> We should be able to list available block devices to set,
>> so the problem would be not avoided anyway.
> 
> Should we? We need to list triggers, but we may not list all the devices...

This is similar to usbport trigger that lists available
ports as files in a sub-directory. We might eventually go
in this direction.

>> And Greg already proposed
>> a solution for trigger file PAGE_SIZE overflow, so this should not pose
>> a big problem in the future once that is implemented.
> 
> Which still leaves us with pretty big/ugly triggers file... and we do
> not have the fix in the tree yet.

Still, we have that interface and must keep it. It implies the fix
will need to be applied anyway.

-- 
Best regards,
Jacek Anaszewski