Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751933AbaFBV6G (ORCPT ); Mon, 2 Jun 2014 17:58:06 -0400 Received: from mail-pd0-f182.google.com ([209.85.192.182]:45563 "EHLO mail-pd0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750941AbaFBV6D (ORCPT ); Mon, 2 Jun 2014 17:58:03 -0400 Message-ID: <1401746280.3645.187.camel@edumazet-glaptop2.roam.corp.google.com> Subject: Re: [PULL 2/2] vhost: replace rcu with mutex From: Eric Dumazet To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, David Miller , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Date: Mon, 02 Jun 2014 14:58:00 -0700 In-Reply-To: <1401744482-17764-3-git-send-email-mst@redhat.com> References: <1401744482-17764-1-git-send-email-mst@redhat.com> <1401744482-17764-3-git-send-email-mst@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-06-03 at 00:30 +0300, Michael S. Tsirkin wrote: > All memory accesses are done under some VQ mutex. > So lock/unlock all VQs is a faster equivalent of synchronize_rcu() > for memory access changes. > Some guests cause a lot of these changes, so it's helpful > to make them faster. > > Reported-by: "Gonglei (Arei)" > Signed-off-by: Michael S. Tsirkin > --- > drivers/vhost/vhost.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 78987e4..1c05e60 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -593,6 +593,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) > { > struct vhost_memory mem, *newmem, *oldmem; > unsigned long size = offsetof(struct vhost_memory, regions); > + int i; > > if (copy_from_user(&mem, m, size)) > return -EFAULT; > @@ -619,7 +620,14 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m) > oldmem = rcu_dereference_protected(d->memory, > lockdep_is_held(&d->mutex)); > rcu_assign_pointer(d->memory, newmem); > - synchronize_rcu(); > + > + /* All memory accesses are done under some VQ mutex. > + * So below is a faster equivalent of synchronize_rcu() > + */ > + for (i = 0; i < d->nvqs; ++i) { > + mutex_lock(&d->vqs[i]->mutex); > + mutex_unlock(&d->vqs[i]->mutex); > + } > kfree(oldmem); > return 0; > } This looks dubious What about using kfree_rcu() instead ? translate_desc() still uses rcu_read_lock(), its not clear if the mutex is really held. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/