linux-kernel - Re: dvb usb issues since kernel 4.9

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Message-ID: <20180113070920.4453eafe@vento.lan>
Date:   Sat, 13 Jan 2018 07:09:20 -0200
From:   Mauro Carvalho Chehab <mchehab@...pensource.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Josef Griebichler <griebichler.josef@....at>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB list <linux-usb@...r.kernel.org>,
        Rik van Riel <riel@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Hannes Frederic Sowa <hannes@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        LMML <linux-media@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: dvb usb issues since kernel 4.9

Em Fri, 12 Jan 2018 13:48:46 -0800
Eric Dumazet <eric.dumazet@...il.com> escreveu:

> On Fri, 2018-01-12 at 19:13 -0200, Mauro Carvalho Chehab wrote:
> > 
> > 
> > The .config file used to build the Kernel is at:
> > 	https://pastebin.com/wpZghann
> > 
> 
> Hi Mauro
> 
> Any chance you can try CONFIG_HZ_1000=y, CONFIG_HZ=1000 ?

I can do such test to satisfy your curiosity, but that doesn't sound the right
fix.

See, almost all TV and set top boxes(STB) run Linux nowadays and usually come
with ARM cpus designed to "just do their job" (e. g. CPUs with low clocks). 
There, power consumption is a must. This bug very likely affect those devices,
once migrated to Kernel 4.9+. Changing from NO_HZ to HZ=1000 on TV/STB will
for sure have bad side effects on those types of devices, increasing power
consumption.

Not saying that this will be environmentally very bad, as the number of just
TV unit sales is at the order of 230 million units per year[1].

[1] https://www.statista.com/statistics/461316/global-tv-unit-sales/


Thanks,
Mauro