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Date: Sat, 24 Oct 2009 10:49:55 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: paulmck@...ux.vnet.ibm.com CC: Octavian Purdila <opurdila@...acom.com>, Benjamin LaHaise <bcrl@...et.ca>, netdev@...r.kernel.org, Cosmin Ratiu <cratiu@...acom.com> Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster Paul E. McKenney a écrit : > On Sat, Oct 24, 2009 at 06:35:53AM +0200, Eric Dumazet wrote: > >> Maybe we could call it once only, if we had to call 1 times >> the jiffie delay ? > > This could be a very useful approach! > > However, please keep in mind that although synchronize_rcu_expedited() > forces a grace period, it does nothing to speed the invocation of other > RCU callbacks. In short, synchronize_rcu_expedited() is a faster version > of synchronize_rcu(), but doesn't necessarily help other synchronize_rcu() > or call_rcu() invocations. > > The reason I point this out is that it looks to me that the code below is > waiting for some other task which is in turn waiting on a grace period. > But I don't know this code, so could easily be confused. > Normally, we need a synchronize_rcu() calls, but I feel its bit more than 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] synchronize_net() 4045596 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.588262] synchronize_net() 7769327 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.625014] synchronize_net() 4772052 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.633008] synchronize_net() 7773896 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.669260] synchronize_net() 3958141 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.677259] synchronize_net() 7755817 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.712011] synchronize_net() 2502544 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.720011] synchronize_net() 7767748 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.754259] synchronize_net() 2087946 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.762258] synchronize_net() 7738054 ns messages:Oct 21 19:13:14 svivoipvnx001-00 kernel: [ 2515.796011] synchronize_net() 3392760 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.808025] synchronize_net() 11814619 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.848010] synchronize_net() 8970220 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.856015] synchronize_net() 7800782 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.893008] synchronize_net() 6650174 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.897012] synchronize_net() 3744808 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.940202] synchronize_net() 8354366 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.952137] synchronize_net() 11693215 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.985010] synchronize_net() 2355970 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2515.989009] synchronize_net() 3771419 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.028137] synchronize_net() 7661195 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.036152] synchronize_net() 7800056 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.083135] synchronize_net() 6774026 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.089145] synchronize_net() 5727189 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.130385] synchronize_net() 10133932 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.134399] synchronize_net() 3773058 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.170136] synchronize_net() 4479194 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.178138] synchronize_net() 7710466 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.217198] synchronize_net() 4323437 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.226206] synchronize_net() 8723108 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.268013] synchronize_net() 6221155 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.280007] synchronize_net() 11719297 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.324008] synchronize_net() 11654511 ns messages:Oct 21 19:13:15 svivoipvnx001-00 kernel: [ 2516.332009] synchronize_net() 7744182 ns -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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