linux-kernel - Re: [PATCH] hrtimer: Update softirq_expires_next correctly after __hrtimer_get_next

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Date:   Wed, 21 Apr 2021 17:22:30 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Lorenzo Colitti <lorenzo@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Maciej Żenczykowski <zenczykowski@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>,
        mikael.beckius@...driver.com,
        Maciej Żenczykowski <maze@...gle.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH] hrtimer: Update softirq_expires_next correctly after
 __hrtimer_get_next_event()

On Wed, Apr 21, 2021 at 11:40:54PM +0900, Lorenzo Colitti wrote:
> On Wed, Apr 21, 2021 at 11:08 PM Lorenzo Colitti <lorenzo@...gle.com> wrote:
> > load the timer will almost never fire since there will always be
> > another packet coming. So the speed of adding/updating the timer is
> > much more important than the accuracy. We will try to move it to
> > timer_list.
> 
> ... but actually, that's not acceptable, because AFAICS timer_list
> counts in jiffies so its resolution might be as low as 10ms. It's not
> acceptable to delay network traffic by up to 10ms under load. Not sure
> if there is another timer API that can be used here.

What do other network drivers do?  This has to be a common problem, why
is this USB driver somehow unique here?

thanks,

greg k-h