linux-kernel - Re: [RFC PATCH 0/2] net: threadable napi poll loop

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Date:	Wed, 11 May 2016 07:45:51 -0700
From:	Eric Dumazet <edumazet@...gle.com>
To:	Paolo Abeni <pabeni@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Pirko <jiri@...lanox.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Alexander Duyck <aduyck@...antis.com>,
	Tom Herbert <tom@...bertland.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/2] net: threadable napi poll loop

On Wed, May 11, 2016 at 7:38 AM, Paolo Abeni <pabeni@...hat.com> wrote:

> Uh, we have likely the same issue in the net_rx_action() function, which
> also execute with bh disabled and check for jiffies changes even on
> single core hosts ?!?

That is why we have a loop break after netdev_budget=300 packets.
And a sysctl to eventually tune this.

Same issue for softirq handler, look at commit
34376a50fb1fa095b9d0636fa41ed2e73125f214

Your questions about this central piece of networking code are worrying.

>
> Aren't jiffies updated by the timer interrupt ? and thous even with
> bh_disabled ?!?

Exactly my point : jiffie wont be updated in your code, since you block BH.