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

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Date:   Tue, 14 Feb 2017 11:29:34 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     netdev@...r.kernel.org, tariqt@...lanox.com, saeedm@...lanox.com
Subject: Re: [PATCH net-next] mlx4: do not fire tasklet unless necessary

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 10 Feb 2017 04:27:58 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> All rx and rx netdev interrupts are handled by respectively
> by mlx4_en_rx_irq() and mlx4_en_tx_irq() which simply schedule a NAPI.
> 
> But mlx4_eq_int() also fires a tasklet to service all items that were
> queued via mlx4_add_cq_to_tasklet(), but this handler was not called
> unless user cqe was handled.
> 
> This is very confusing, as "mpstat -I SCPU ..." show huge number of
> tasklet invocations.
> 
> This patch saves this overhead, by carefully firing the tasklet directly
> from mlx4_add_cq_to_tasklet(), removing four atomic operations per IRQ.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Tariq Toukan <tariqt@...lanox.com>
> Cc: Saeed Mahameed <saeedm@...lanox.com>

Tariq/Saeed, please review.