From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] vhost_net: stop polling socket during rx processing Date: Wed, 27 Apr 2016 14:28:38 +0300 Message-ID: <20160427141317-mutt-send-email-mst@redhat.com> References: <1461656153-24074-1-git-send-email-jasowang@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: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <1461656153-24074-1-git-send-email-jasowang@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 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. ---> 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);