netdev - RE: [PATCH net-next v2 0/5] implement kthread based napi poll

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Date:   Sat, 3 Oct 2020 10:56:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Wei Wang' <weiwan@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Felix Fietkau <nbd@....name>
Subject: RE: [PATCH net-next v2 0/5] implement kthread based napi poll

From: Wei Wang
> Sent: 02 October 2020 23:25
> 
> The idea of moving the napi poll process out of softirq context to a
> kernel thread based context is not new.
> Paolo Abeni and Hannes Frederic Sowa have proposed patches to move napi
> poll to kthread back in 2016. And Felix Fietkau has also proposed
> patches of similar ideas to use workqueue to process napi poll just a
> few weeks ago.

I didn't spot anything that makes this continue to work?

static inline bool netdev_xmit_more(void)
{
        return __this_cpu_read(softnet_data.xmit.more);
}

I assume it normally relies on the softint code running with
pre-emption disabled.

(It also needs a level of indirection.
xmit.more is only set if more packets are queued when the tx
call is done.
I've seen a workload that manages to repeatedly add an extra
packet while the tx setup is in progress.)

	David

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