| Message ID | 20160427141317-mutt-send-email-mst@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 04/27/2016 07:28 PM, Michael S. Tsirkin wrote: > On Tue, Apr 26, 2016 at 03:35:53AM -0400, Jason Wang wrote: >> We don't stop polling socket during rx processing, this will lead >> unnecessary wakeups from under layer net devices (E.g >> sock_def_readable() form tun). Rx will be slowed down in this >> way. This patch avoids this by stop polling socket during rx >> processing. A small drawback is that this introduces some overheads in >> light load case because of the extra start/stop polling, but single >> netperf TCP_RR does not notice any change. In a super heavy load case, >> e.g using pktgen to inject packet to guest, we get about ~17% >> improvement on pps: >> >> before: ~1370000 pkt/s >> after: ~1500000 pkt/s >> >> Signed-off-by: Jason Wang <jasowang@redhat.com> > Acked-by: Michael S. Tsirkin <mst@redhat.com> > > There is one other possible enhancement: we actually have the wait queue > lock taken in _wake_up, but we give it up only to take it again in the > handler. > > It would be nicer to just remove the entry when we wake > the vhost thread. Re-add it if required. > I think that something like the below would give you the necessary API. > Pls feel free to use it if you are going to implement a patch on top > doing this - that's not a reason not to include this simple patch > though. Thanks, this looks useful, will give it a try. > > ---> > > wait: add API to drop a wait_queue_t entry from wake up handler > > A wake up handler might want to remove its own wait queue entry to avoid > future wakeups. In particular, vhost has such a need. As wait queue > lock is already taken, all we need is an API to remove the entry without > wait_queue_head_t which isn't currently accessible to wake up handlers. > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > --- > > diff --git a/include/linux/wait.h b/include/linux/wait.h > index 27d7a0a..9c6604b 100644 > --- a/include/linux/wait.h > +++ b/include/linux/wait.h > @@ -191,11 +191,17 @@ __add_wait_queue_tail_exclusive(wait_queue_head_t *q, wait_queue_t *wait) > } > > static inline void > -__remove_wait_queue(wait_queue_head_t *head, wait_queue_t *old) > +__remove_wait_queue_entry(wait_queue_t *old) > { > list_del(&old->task_list); > } > > +static inline void > +__remove_wait_queue(wait_queue_head_t *head, wait_queue_t *old) > +{ > + __remove_wait_queue_entry(old); > +} > + > typedef int wait_bit_action_f(struct wait_bit_key *, int mode); > void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr, void *key); > void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key); -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 04/28/2016 02:19 PM, Jason Wang wrote: > On 04/27/2016 07:28 PM, Michael S. Tsirkin wrote: >> > On Tue, Apr 26, 2016 at 03:35:53AM -0400, Jason Wang wrote: >>> >> We don't stop polling socket during rx processing, this will lead >>> >> unnecessary wakeups from under layer net devices (E.g >>> >> sock_def_readable() form tun). Rx will be slowed down in this >>> >> way. This patch avoids this by stop polling socket during rx >>> >> processing. A small drawback is that this introduces some overheads in >>> >> light load case because of the extra start/stop polling, but single >>> >> netperf TCP_RR does not notice any change. In a super heavy load case, >>> >> e.g using pktgen to inject packet to guest, we get about ~17% >>> >> improvement on pps: >>> >> >>> >> before: ~1370000 pkt/s >>> >> after: ~1500000 pkt/s >>> >> >>> >> Signed-off-by: Jason Wang <jasowang@redhat.com> >> > Acked-by: Michael S. Tsirkin <mst@redhat.com> >> > >> > There is one other possible enhancement: we actually have the wait queue >> > lock taken in _wake_up, but we give it up only to take it again in the >> > handler. >> > >> > It would be nicer to just remove the entry when we wake >> > the vhost thread. Re-add it if required. >> > I think that something like the below would give you the necessary API. >> > Pls feel free to use it if you are going to implement a patch on top >> > doing this - that's not a reason not to include this simple patch >> > though. > Thanks, this looks useful, will give it a try. Want to try, but looks like this will result a strange API: - poll were removed automatically during wakeup, handler does not need to care about this - but handler still need to re-add the poll explicitly in the code ? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/wait.h b/include/linux/wait.h index 27d7a0a..9c6604b 100644 --- a/include/linux/wait.h +++ b/include/linux/wait.h @@ -191,11 +191,17 @@ __add_wait_queue_tail_exclusive(wait_queue_head_t *q, wait_queue_t *wait) } static inline void -__remove_wait_queue(wait_queue_head_t *head, wait_queue_t *old) +__remove_wait_queue_entry(wait_queue_t *old) { list_del(&old->task_list); } +static inline void +__remove_wait_queue(wait_queue_head_t *head, wait_queue_t *old) +{ + __remove_wait_queue_entry(old); +} + typedef int wait_bit_action_f(struct wait_bit_key *, int mode); void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr, void *key); void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key);