netdev - Re: [PATCH net-next] mlx4: do not fire tasklet unless necessary

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Message-ID: <1487167443.1311.8.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 15 Feb 2017 06:04:03 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Saeed Mahameed <saeedm@....mellanox.co.il>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Matan Barak <matanb@...lanox.com>, jackm@...lanox.com
Subject: Re: [PATCH net-next] mlx4: do not fire tasklet unless necessary

On Wed, 2017-02-15 at 05:29 -0800, Eric Dumazet wrote:

> 
> mlx4_eq_int() is a hard irq handler.
> 
> How a tasklet could run in the middle of it ?
> 
> A tasklet is a softirq handler.

Speaking of mlx4_eq_int() , 50% of cycles are spent on mb() (mfence)
in eq_set_ci()

I wonder why this very expensive mb() is required, right before exiting
the interrupt handler.