Re: [PATCH] usb: don't offload isochronous urb completions to ksoftirq

From: Alan Stern
Date: Tue Jun 12 2018 - 12:38:54 EST

On Tue, 12 Jun 2018, Mikulas Patocka wrote:

> > How about making the softirq thread's priority adjustable?
> But you would have to argue with softirq maintainers about it - and you
> say that you don't have time for that.

But maybe _you_ do...

> > As for coordinating with the softirq maintainers -- whether I want to
> > or not isn't the issue. Right now I don't have _time_ to do it.
> >
> > Alan Stern
> I am wondering - whats the purpose of that patch
> 428aac8a81058e2303677a8fbf26670229e51d3a at all? The patch shows some
> performance difference, but they are minor, about 1%.
> If you want to call the urb callback as soon as possible - why don't you
> just call it? Why do you need to offload the callback to a softirq thread?

Please read the Changelog entry for commit 94dfd7edfd5c. Basically the
idea was to reduce overall latency by not doing as much work in an
interrupt handler.

Alan Stern