Message ID | 1479169722.8455.108.camel@edumazet-glaptop3.roam.corp.google.com |
---|---|
State | Accepted, archived |
Delegated to: | David Miller |
Headers | show |
On Mon, Nov 14, 2016 at 4:28 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > From: Eric Dumazet <edumazet@google.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@google.com> > Reported-by: Rolf Neugebauer <rolf.neugebauer@docker.com> > Reported-by: Eric W. Biederman <ebiederm@xmission.com> Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
On Tue, Nov 15, 2016 at 12:28 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > From: Eric Dumazet <edumazet@google.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. 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 <edumazet@google.com> > Reported-by: Rolf Neugebauer <rolf.neugebauer@docker.com> > Reported-by: Eric W. Biederman <ebiederm@xmission.com> Tested-by: Rolf Neugebauer <rolf.neugebauer@docker.com> > --- > 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); > } > >
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Mon, 14 Nov 2016 16:28:42 -0800 > From: Eric Dumazet <edumazet@google.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@google.com> > Reported-by: Rolf Neugebauer <rolf.neugebauer@docker.com> > Reported-by: Eric W. Biederman <ebiederm@xmission.com> Applied, thanks.
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); }