netdev - Re: [WIP] net+mlx4: auto doorbell

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Message-ID: <1480534200.18162.203.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 30 Nov 2016 11:30:00 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Rick Jones <rick.jones2@....com>, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Achiad Shochat <achiad@...lanox.com>
Subject: Re: [WIP] net+mlx4: auto doorbell

On Wed, 2016-11-30 at 20:17 +0100, Jesper Dangaard Brouer wrote:

> Don't take is as critique Eric.  I was hoping your patch would have
> solved this issue of being sensitive to TX completion adjustments.  You
> usually have good solutions for difficult issues. I basically rejected
> Achiad's approach/patch because it was too sensitive to these kind of
> adjustments.

Well, this patch can hurt latencies, because a doorbell can be delayed,
and softirqs can be delayed by many hundred of usec in some cases.

I would not enable this behavior by default.