Re: [PATCH 1/3] parisc: led: Reduce CPU overhead for disk & lan LED computation

[Helge Deller <deller@gmx.de>]

On 8/26/23 09:58, Greg KH wrote:
> On Sat, Aug 26, 2023 at 09:54:55AM +0200, Helge Deller wrote:
>> On 8/26/23 09:34, Greg KH wrote:
>>> On Fri, Aug 25, 2023 at 08:09:26PM +0200, deller@kernel.org wrote:
>>>> From: Helge Deller <deller@gmx.de>
>>>>
>>>> Older PA-RISC machines have LEDs which show the disk- and LAN-activity.
>>>> The computation is done in software and takes quite some time, e.g. on a
>>>> J6500 this may take up to 60% time of one CPU if the machine is loaded
>>>> via network traffic.
>>>>
>>>> Since most people don't care about the LEDs, start with LEDs disabled and
>>>> just show a CPU heartbeat LED. The disk and LAN LEDs can be turned on
>>>> manually via /proc/pdc/led.
>>>>
>>>> Signed-off-by: Helge Deller <deller@gmx.de>
>>>> Cc: <stable@vger.kernel.org>
>>>> ---
>>>>    drivers/parisc/led.c | 7 +++++--
>>>>    1 file changed, 5 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/parisc/led.c b/drivers/parisc/led.c
>>>> index 8bdc5e043831..765f19608f60 100644
>>>> --- a/drivers/parisc/led.c
>>>> +++ b/drivers/parisc/led.c
>>>> @@ -56,8 +56,8 @@
>>>>    static int led_type __read_mostly = -1;
>>>>    static unsigned char lastleds;	/* LED state from most recent update */
>>>>    static unsigned int led_heartbeat __read_mostly = 1;
>>>> -static unsigned int led_diskio    __read_mostly = 1;
>>>> -static unsigned int led_lanrxtx   __read_mostly = 1;
>>>> +static unsigned int led_diskio    __read_mostly;
>>>> +static unsigned int led_lanrxtx   __read_mostly;
>>>>    static char lcd_text[32]          __read_mostly;
>>>>    static char lcd_text_default[32]  __read_mostly;
>>>>    static int  lcd_no_led_support    __read_mostly = 0; /* KittyHawk doesn't support LED on its LCD */
>>>> @@ -589,6 +589,9 @@ int __init register_led_driver(int model, unsigned long cmd_reg, unsigned long d
>>>>    		return 1;
>>>>    	}
>>>>
>>>> +	pr_info("LED: Enable disk and LAN activity LEDs "
>>>> +		"via /proc/pdc/led\n");
>>>
>>> When drivers are working properly, they should be quiet.  Who is going
>>> to see this message?
>>
>> That patch shouldn't have gone to stable@ yet... git-send-patch just
>> pulled the CC in and I didn't noticed.
>> So, please don't apply it yet.
>
> I will not, and it's fine to cc: stable@ on stuff that is still making
> it's way into the kernel tree.  It gives us a heads-up on stuff, AND
> sometimes it gives you an additional free review :)

Yes, thanks!  :-)

>>> I don't even understand it, are you saying that you now need to go
>>> enable the led through proc?  And why are leds in proc, I thought they
>>> had a real class for them?  Why not use that instead?
>>
>> This is an old driver from the very beginning, and I don't want to change
>> much in it for old kernels other than to reduce the CPU overhead it generates.
>
> Ah, makes sense, that is a crazy amount of cpu time for a blinking led.
>
> How about just default to it off (like the first chunk you have here),
> which will go to stable trees,

Yes, that was the idea of this patch. I'll drop the pr_info() next time.

> and then a rewrite to use the proper LED api?

Yes.

Helge