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

From: Pavel Machek <pavel@ucw.cz>
To: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>,
	linux-block@vger.kernel.org, linux-leds@vger.kernel.org,
	linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org,
	Frank Steiner <fsteiner-mail1@bio.ifi.lmu.de>,
	Dan Murphy <dmurphy@ti.com>, Jens Axboe <axboe@kernel.dk>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Hannes Reinecke <hare@suse.com>
Subject: Re: [PATCH v4 4/5] block: introduce LED block device activity trigger
Date: Mon, 19 Aug 2019 16:38:42 +0200	[thread overview]
Message-ID: <20190819143842.GA25401@amd> (raw)
In-Reply-To: <925633c4-a459-5e84-9c9a-502a504fdc82@gmail.com>

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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...

> 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.

Best regards,

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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