Hello Pavel, Do you have any feedback/thoughts about this one? The problem looks very bad, Load Average value should not grow up due to any userspace triggered led animation. I suppose we stronlgy need to fixup this behavior for sure. Appreciate any help! On Mon, Oct 31, 2022 at 05:47:04PM +0300, Dmitry Rokosov wrote: > Hello Pavel and Arseniy, > > Please find my thoughts below. > > On Mon, Oct 31, 2022 at 10:01:28AM +0300, Arseniy Krasnov wrote: > > On 30.10.2022 23:15, Pavel Machek wrote: > > > Hi! > > > > > >>>> This allows to set own workqueue for each LED. This may be useful, because > > >>>> default 'system_wq' does not guarantee execution order of each work_struct, > > >>>> thus for several brightness update requests (for multiple leds), real > > >>>> brightness switch could be in random order. > > >>> > > >>> So.. what? > > >>> > > >>> Even if execution order is switched, human eye will not be able to > > >>> tell the difference. > > >> Hello, > > >> > > >> Problem arises on one of our boards where we have 14 triples of leds(each > > >> triple contains R G B). Test case is to play complex animation on all leds: > > >> smooth switch from on RGB state to another. Sometimes there are glitches in > > >> this process - divergence from expectable RGB state. We fixed this by using > > >> ordered workqueue. > > > > > > Are there other solutions possible? Like batch and always apply _all_ > > > the updates you have queued from your the worker code? > > > > IIUC You, it is possible to do this if brightness update requests are performed using > > write to "brightness" file in /sys/class/led/. But if pattern trigger mode is used(in my > > case) - I can't synchronize these requests as they are created internally in kernel on > > timer tick. > > Even more, system_wq is used when you push brightness changing requests > to sysfs node, and it could be re-ordered as well. In other words, from > queue perspective sysfs iface and trigger iface have the same behavior. > > Also we can be faced with another big problem here: let's imagine you have > I2C based LED controller driver. Usually, in such drivers you're stuck > to the one driver owned mutex, which protects I2C transactions from each > other. > > When you change brightness very often (let's say a hundred thousand times > per minute) you schedule many workers to system_wq. Due to system_wq is > multicore and unordered it creates many kworkers. Each kworker stucks on > the driver mutex and goes to TASK_UNINTERRUPTIBLE state. It affects Load > Average value so much. On the our device LA maximum could reach 30-35 > units due to such idle kworkers. > > I'm not sure custom workqueue initialization from specific HW driver is > a good solution... But it's much better than nothing. > > Pavel, please share your thoughts about above problems? Maybe you have > more advanced and scalable solution idea, I would appreciate if you > could share it with us. -- Thank you, Dmitry
