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

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Message-ID: <20180615124609.7726924b@gandalf.local.home>
Date:   Fri, 15 Jun 2018 12:46:09 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ming Lei <ming.lei@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB list <linux-usb@...r.kernel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: don't offload isochronous urb completions to
 ksoftirq

On Fri, 15 Jun 2018 12:41:10 -0400 (EDT)
Mikulas Patocka <mpatocka@...hat.com> wrote:

> BTW. when I subject the machine to a ping flood (ping -f), the 
> non-realtime kernel (with the patch to avoid offloading ehci urb 
> callbacks) performs better than the real-time kernel.
> 
> With the real-time kernel, all the networking work is done in the thread 
> "irq/12-eth0", that has (by default) priority -51, it consumes 30% CPU 
> time and causes sound skipping. I can avoid the skipping by lowering the 
> priority of "irq/12-eth0".

That's actually the correct thing to do. When dealing with RT
applications, one needs to modify the priority of the interrupts that
are required (or lower the ones that are not).

> 
> With non-realtime kernel, no such problem during ping flood exists.

But that was with a patched kernel?

-- Steve