From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster Date: Sat, 24 Oct 2009 13:22:38 -0700 Message-ID: <20091024132238.35069740@nehalam> References: <20091017221857.GG1925@kvack.org> <4ADB55BC.5020107@gmail.com> <20091018182144.GC23395@kvack.org> <200910211539.01824.opurdila@ixiacom.com> <4ADF2B57.4030708@gmail.com> <20091023211338.GA6145@linux.vnet.ibm.com> <4AE28429.6040608@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: paulmck@linux.vnet.ibm.com, Octavian Purdila , Benjamin LaHaise , netdev@vger.kernel.org, Cosmin Ratiu To: Eric Dumazet Return-path: Received: from mail.vyatta.com ([76.74.103.46]:55492 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751864AbZJXUWj convert rfc822-to-8bit (ORCPT ); Sat, 24 Oct 2009 16:22:39 -0400 In-Reply-To: <4AE28429.6040608@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On Sat, 24 Oct 2009 06:35:53 +0200 Eric Dumazet wrote: > Paul E. McKenney a =C3=A9crit : > > On Wed, Oct 21, 2009 at 05:40:07PM +0200, Eric Dumazet wrote: > >> [PATCH] net: allow netdev_wait_allrefs() to run faster > >> > >> netdev_wait_allrefs() waits that all references to a device vanish= es. > >> > >> It currently uses a _very_ pessimistic 250 ms delay between each p= robe. > >> Some users report that no more than 4 devices can be dismantled pe= r second, > >> this is a pretty serious problem for extreme setups. > >> > >> Most likely, references only wait for a rcu grace period that shou= ld come > >> fast, so use a schedule_timeout_uninterruptible(1) to allow faster= recovery. > >=20 > > Is this a place where synchronize_rcu_expedited() is appropriate? > > (It went in to 2.6.32-rc1.) > >=20 >=20 > Thanks for the tip Paul >=20 > I believe netdev_wait_allrefs() is not a perfect candidate, because=20 > synchronize_sched_expedited() seems really expensive. >=20 > Maybe we could call it once only, if we had to call 1 times > the jiffie delay ? >=20 > diff --git a/net/core/dev.c b/net/core/dev.c > index fa88dcd..9b04b9a 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -4970,6 +4970,7 @@ EXPORT_SYMBOL(register_netdev); > static void netdev_wait_allrefs(struct net_device *dev) > { > unsigned long rebroadcast_time, warning_time; > + unsigned int count =3D 0; > =20 > rebroadcast_time =3D warning_time =3D jiffies; > while (atomic_read(&dev->refcnt) !=3D 0) { > @@ -4995,7 +4996,10 @@ static void netdev_wait_allrefs(struct net_dev= ice *dev) > rebroadcast_time =3D jiffies; > } > =20 > - msleep(250); > + if (count++ =3D=3D 1) > + synchronize_rcu_expedited(); > + else > + schedule_timeout_uninterruptible(1); > =20 > if (time_after(jiffies, warning_time + 10 * HZ)) { > printk(KERN_EMERG "unregister_netdevice: " Actually, anything that requires more than one pass through the loop is broken. Devices and protocols should be cleaning up on the first notifi= er. The worst offender seems to be the dst cache gc code. --=20