netdev - Re: [PATCH net] gro_cells: mark napi struct as not busy poll candidates

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Date:   Tue, 15 Nov 2016 22:29:13 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     ebiederm@...ssion.com, paulmck@...ux.vnet.ibm.com,
        xiyou.wangcong@...il.com, rolf.neugebauer@...ker.com,
        netdev@...r.kernel.org, justin.cormack@...ker.com,
        ian.campbell@...ker.com, edumazet@...gle.com
Subject: Re: [PATCH net] gro_cells: mark napi struct as not busy poll
 candidates

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 14 Nov 2016 16:28:42 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Rolf Neugebauer reported very long delays at netns dismantle.
> 
> Eric W. Biederman was kind enough to look at this problem
> and noticed synchronize_net() occurring from netif_napi_del() that was
> added in linux-4.5
> 
> Busy polling makes no sense for tunnels NAPI.
> If busy poll is used for sessions over tunnels, the poller will need to
> poll the physical device queue anyway.
> 
> netif_tx_napi_add() could be used here, but function name is misleading,
> and renaming it is not stable material, so set NAPI_STATE_NO_BUSY_POLL
> bit directly.
> 
> This will avoid inserting gro_cells napi structures in napi_hash[]
> and avoid the problematic synchronize_net() (per possible cpu) that
> Rolf reported.
> 
> Fixes: 93d05d4a320c ("net: provide generic busy polling to all NAPI drivers")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Rolf Neugebauer <rolf.neugebauer@...ker.com>
> Reported-by: Eric W. Biederman <ebiederm@...ssion.com>

Applied, thanks.