On Tue, Nov 15, 2016 at 12:28 AM, Eric Dumazet <[email protected]> wrote:
> From: Eric Dumazet <[email protected]>
>
> 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.
Thanks for the quick turn-around. I've tested this on both 4.9-rc5 and
4.8.7 with different CPU configs and it dramatically reduced the
delay. I still see a small (1s) delay for creating a new namespace
after deleting one in one config but will follow up with the details
on the original email thread.
>
> Fixes: 93d05d4a320c ("net: provide generic busy polling to all NAPI drivers")
> Signed-off-by: Eric Dumazet <[email protected]>
> Reported-by: Rolf Neugebauer <[email protected]>
> Reported-by: Eric W. Biederman <[email protected]>
Tested-by: Rolf Neugebauer <[email protected]>
> ---
> include/net/gro_cells.h | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/include/net/gro_cells.h b/include/net/gro_cells.h
> index
> d15214d673b2e8e08fd6437b572278fb1359f10d..2a1abbf8da74368cd01adc40cef6c0644e059ef2
> 100644
> --- a/include/net/gro_cells.h
> +++ b/include/net/gro_cells.h
> @@ -68,6 +68,9 @@ static inline int gro_cells_init(struct gro_cells *gcells,
> struct net_device *de
> struct gro_cell *cell = per_cpu_ptr(gcells->cells, i);
>
> __skb_queue_head_init(&cell->napi_skbs);
> +
> + set_bit(NAPI_STATE_NO_BUSY_POLL, &cell->napi.state);
> +
> netif_napi_add(dev, &cell->napi, gro_cell_poll, 64);
> napi_enable(&cell->napi);
> }
>
>
