From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH] vhost_net: stop polling socket during rx processing Date: Thu, 28 Apr 2016 14:19:39 +0800 Message-ID: <5721AB7B.8070806@redhat.com> References: <1461656153-24074-1-git-send-email-jasowang@redhat.com> <20160427141317-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20160427141317-mutt-send-email-mst@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org 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 > Acked-by: Michael S. Tsirkin > > 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 > > --- > > 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);