netdev - Re: [net-next PATCH v2 5/8] net: Track start of busy loop instead of when it should end

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Message-ID: <1490318682.9687.22.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 23 Mar 2017 18:24:42 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        sridhar.samudrala@...el.com, edumazet@...gle.com,
        davem@...emloft.net, linux-api@...r.kernel.org
Subject: Re: [net-next PATCH v2 5/8] net: Track start of busy loop instead
 of when it should end

On Thu, 2017-03-23 at 14:37 -0700, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@...el.com>
> 

> The last bit I changed is to move from using a shift by 10 to just using
> NSEC_PER_USEC and using multiplication for any run time calculations and
> division for a few compile time ones.  This should be more accurate and
> perform about the same on most architectures since modern CPUs typically
> handle multiplication without too much overhead.


busy polling thread can be preempted for more than 2 seconds.

Using usec instead of nanoseconds gave us 3 orders of magnitude cushion.

We do not need nsec accuracy for busy polling users, if this restricts
range and usability under stress.