From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster Date: Sat, 24 Oct 2009 10:49:55 +0200 Message-ID: <4AE2BFB3.3060407@gmail.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> 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: paulmck@linux.vnet.ibm.com Return-path: Received: from gw1.cosmosbay.com ([212.99.114.194]:48887 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752218AbZJXIuK (ORCPT ); Sat, 24 Oct 2009 04:50:10 -0400 In-Reply-To: <20091024054943.GA6638@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: 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_expedited(= ) > forces a grace period, it does nothing to speed the invocation of oth= er > RCU callbacks. In short, synchronize_rcu_expedited() is a faster ver= sion > of synchronize_rcu(), but doesn't necessarily help other synchronize_= rcu() > or call_rcu() invocations. >=20 > The reason I point this out is that it looks to me that the code belo= w is > waiting for some other task which is in turn waiting on a grace perio= d. > But I don't know this code, so could easily be confused. >=20 Normally, we need a synchronize_rcu() calls, but I feel its bit more th= an really needed here. On my dev machine, a synchronize_rcu() lasts between 2 an 12 ms messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.580259] synchr= onize_net() 4045596 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.588262] synchr= onize_net() 7769327 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.625014] synchr= onize_net() 4772052 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.633008] synchr= onize_net() 7773896 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.669260] synchr= onize_net() 3958141 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.677259] synchr= onize_net() 7755817 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.712011] synchr= onize_net() 2502544 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.720011] synchr= onize_net() 7767748 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.754259] synchr= onize_net() 2087946 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.762258] synchr= onize_net() 7738054 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.796011] synchr= onize_net() 3392760 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.808025] synchr= onize_net() 11814619 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.848010] synchr= onize_net() 8970220 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.856015] synchr= onize_net() 7800782 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.893008] synchr= onize_net() 6650174 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.897012] synchr= onize_net() 3744808 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.940202] synchr= onize_net() 8354366 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.952137] synchr= onize_net() 11693215 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.985010] synchr= onize_net() 2355970 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.989009] synchr= onize_net() 3771419 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.028137] synchr= onize_net() 7661195 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.036152] synchr= onize_net() 7800056 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.083135] synchr= onize_net() 6774026 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.089145] synchr= onize_net() 5727189 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.130385] synchr= onize_net() 10133932 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.134399] synchr= onize_net() 3773058 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.170136] synchr= onize_net() 4479194 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.178138] synchr= onize_net() 7710466 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.217198] synchr= onize_net() 4323437 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.226206] synchr= onize_net() 8723108 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.268013] synchr= onize_net() 6221155 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.280007] synchr= onize_net() 11719297 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.324008] synchr= onize_net() 11654511 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.332009] synchr= onize_net() 7744182 ns