From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster Date: Sat, 24 Oct 2009 06:52:14 -0700 Message-ID: <20091024135214.GB6638@linux.vnet.ibm.com> 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> <20091024054943.GA6638@linux.vnet.ibm.com> <4AE2BFB3.3060407@gmail.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Octavian Purdila , Benjamin LaHaise , netdev@vger.kernel.org, Cosmin Ratiu To: Eric Dumazet Return-path: Received: from e4.ny.us.ibm.com ([32.97.182.144]:60974 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753506AbZJXNwL (ORCPT ); Sat, 24 Oct 2009 09:52:11 -0400 Received: from d01relay07.pok.ibm.com (d01relay07.pok.ibm.com [9.56.227.147]) by e4.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id n9ODiQEX032429 for ; Sat, 24 Oct 2009 09:44:26 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay07.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id n9ODqFJD1048774 for ; Sat, 24 Oct 2009 09:52:15 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id n9ODqEXA006617 for ; Sat, 24 Oct 2009 09:52:15 -0400 Content-Disposition: inline In-Reply-To: <4AE2BFB3.3060407@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On Sat, Oct 24, 2009 at 10:49:55AM +0200, Eric Dumazet wrote: > Paul E. McKenney a =E9crit : > > On Sat, Oct 24, 2009 at 06:35:53AM +0200, Eric Dumazet wrote: > >=20 > >> Maybe we could call it once only, if we had to call 1 times > >> the jiffie delay ? > >=20 > > This could be a very useful approach! > >=20 > > However, please keep in mind that although synchronize_rcu_expedite= d() > > forces a grace period, it does nothing to speed the invocation of o= ther > > RCU callbacks. In short, synchronize_rcu_expedited() is a faster v= ersion > > of synchronize_rcu(), but doesn't necessarily help other synchroniz= e_rcu() > > or call_rcu() invocations. > >=20 > > The reason I point this out is that it looks to me that the code be= low is > > waiting for some other task which is in turn waiting on a grace per= iod. > > But I don't know this code, so could easily be confused. > >=20 >=20 > Normally, we need a synchronize_rcu() calls, but I feel its bit more = than really > needed here. >=20 > On my dev machine, a synchronize_rcu() lasts between 2 an 12 ms That sounds like the right range, depending on what else is happening on the machine at the time. The synchronize_rcu_expedited() primitive would run in the 10s-100s of microseconds. It involves a pair of wakeups and a pair of context switches on each CPU. Thanx, Paul > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.580259] sync= hronize_net() 4045596 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.588262] sync= hronize_net() 7769327 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.625014] sync= hronize_net() 4772052 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.633008] sync= hronize_net() 7773896 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.669260] sync= hronize_net() 3958141 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.677259] sync= hronize_net() 7755817 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.712011] sync= hronize_net() 2502544 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.720011] sync= hronize_net() 7767748 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.754259] sync= hronize_net() 2087946 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.762258] sync= hronize_net() 7738054 ns > messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.796011] sync= hronize_net() 3392760 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.808025] sync= hronize_net() 11814619 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.848010] sync= hronize_net() 8970220 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.856015] sync= hronize_net() 7800782 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.893008] sync= hronize_net() 6650174 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.897012] sync= hronize_net() 3744808 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.940202] sync= hronize_net() 8354366 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.952137] sync= hronize_net() 11693215 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.985010] sync= hronize_net() 2355970 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.989009] sync= hronize_net() 3771419 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.028137] sync= hronize_net() 7661195 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.036152] sync= hronize_net() 7800056 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.083135] sync= hronize_net() 6774026 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.089145] sync= hronize_net() 5727189 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.130385] sync= hronize_net() 10133932 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.134399] sync= hronize_net() 3773058 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.170136] sync= hronize_net() 4479194 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.178138] sync= hronize_net() 7710466 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.217198] sync= hronize_net() 4323437 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.226206] sync= hronize_net() 8723108 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.268013] sync= hronize_net() 6221155 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.280007] sync= hronize_net() 11719297 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.324008] sync= hronize_net() 11654511 ns > messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.332009] sync= hronize_net() 7744182 ns >=20