Re: Re: dvb usb issues since kernel 4.9

[Linus Torvalds]

On Tue, Jan 9, 2018 at 9:57 AM, Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> Your patch considers TASKLET_SOFTIRQ being a candidate for 'immediate
> handling', but TCP Small queues heavily use TASKLET,
> so as far as I am concerned a revert would have the same effect.

Does it actually?

TCP ends up dropping packets outside of the window etc, so flooding a
machine with TCP packets and causing some further processing up the
stack sounds very different from the basic packet flooding thing that
happens with NET_RX_SOFTIRQ.

Also, honestly, the kinds of people who really worry about flooding
tend to have packet filtering in the receive path etc.

So I really think "you can use up 90% of CPU time with a UDP packet
flood from the same network" is very very very different - and
honestly not at all as important - as "you want to be able to use a
USB DVB receiver and watch/record TV".

Because that whole "UDP packet flood from the same network" really is
something you _fundamentally_ have other mitigations for.

I bet that whole commit was introduced because of a benchmark test,
rather than real life. No?

In contrast, now people are complaining about real loads not working.

             Linus