netdev - Re: [PATCH] net: less interrupt masking in NAPI

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Date:	Mon, 03 Nov 2014 12:25:38 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, willemb@...gle.com
Subject: Re: [PATCH] net: less interrupt masking in NAPI

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sun, 02 Nov 2014 06:19:33 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> net_rx_action() can mask irqs a single time to transfert sd->poll_list
> into a private list, for a very short duration.
> 
> Then, napi_complete() can avoid masking irqs again,
> and net_rx_action() only needs to mask irq again in slow path.
> 
> This patch removes 2 couples of irq mask/unmask per typical NAPI run,
> more if multiple napi were triggered.
> 
> Note this also allows to give control back to caller (do_softirq())
> more often, so that other softirq handlers can be called a bit earlier,
> or ksoftirqd can be wakeup earlier under pressure.
> 
> This was developed while testing an alternative to RX interrupt
> mitigation to reduce latencies while keeping or improving GRO
> aggregation on fast NIC.
> 
> Idea is to test napi->gro_list at the end of a napi->poll() and
> reschedule one NAPI poll, but after servicing a full round of
> softirqs (timers, TX, rcu, ...). This will be allowed only if softirq
> is currently serviced by idle task or ksoftirqd, and resched not needed.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Also applied, thanks Eric.
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