Re: [PATCH] net: allow netdev_wait_allrefs() to run faster

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From: Eric Dumazet

Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster

Date: Saturday, October 24, 2009 - 1:49 am

Paul E. McKenney a écrit :
quoted text> 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

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Messages in current thread:

[PATCH/RFC] make unregister_netdev() delete more than 4 in ..., Benjamin LaHaise, (Sat Oct 17, 3:18 pm)

Re: [PATCH/RFC] make unregister_netdev() delete more than ..., Eric Dumazet, (Sat Oct 17, 9:26 pm)

Re: [PATCH/RFC] make unregister_netdev() delete more than ..., Benjamin LaHaise, (Sun Oct 18, 9:13 am)

Re: [PATCH/RFC] make unregister_netdev() delete more than ..., Eric Dumazet, (Sun Oct 18, 10:51 am)

Re: [PATCH/RFC] make unregister_netdev() delete more than ..., Benjamin LaHaise, (Sun Oct 18, 11:21 am)

Re: [PATCH/RFC] make unregister_netdev() delete more than ..., Eric Dumazet, (Sun Oct 18, 12:36 pm)

Re: [PATCH/RFC] make unregister_netdev() delete more than ..., Octavian Purdila, (Wed Oct 21, 5:39 am)

[PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Wed Oct 21, 8:40 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Wed Oct 21, 9:09 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Benjamin LaHaise, (Wed Oct 21, 9:51 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Octavian Purdila, (Wed Oct 21, 9:55 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Wed Oct 21, 12:54 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Paul E. McKenney, (Fri Oct 23, 2:13 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Fri Oct 23, 9:35 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Paul E. McKenney, (Fri Oct 23, 10:49 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Sat Oct 24, 1:49 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Paul E. McKenney, (Sat Oct 24, 6:52 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Sat Oct 24, 7:24 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Paul E. McKenney, (Sat Oct 24, 7:46 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Stephen Hemminger, (Sat Oct 24, 1:22 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Octavian Purdila, (Sat Oct 24, 4:49 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Paul E. McKenney, (Sat Oct 24, 9:47 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Sun Oct 25, 1:35 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Octavian Purdila, (Sun Oct 25, 8:19 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Sun Oct 25, 12:28 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric W. Biederman, (Thu Oct 29, 4:07 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Benjamin LaHaise, (Thu Oct 29, 4:38 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric W. Biederman, (Thu Oct 29, 6:45 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Benjamin LaHaise, (Fri Oct 30, 7:35 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric Dumazet, (Fri Oct 30, 7:43 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric W. Biederman, (Fri Oct 30, 4:25 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Benjamin LaHaise, (Fri Oct 30, 4:53 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric W. Biederman, (Fri Oct 30, 5:37 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Ben Greear, (Mon Aug 9, 10:23 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Benjamin LaHaise, (Mon Aug 9, 10:34 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Ben Greear, (Mon Aug 9, 10:44 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Benjamin LaHaise, (Mon Aug 9, 10:48 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Ben Greear, (Mon Aug 9, 11:03 am)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric W. Biederman, (Mon Aug 9, 12:59 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Benjamin LaHaise, (Mon Aug 9, 2:03 pm)

Re: [PATCH] net: allow netdev_wait_allrefs() to run faster, Eric W. Biederman, (Mon Aug 9, 2:17 pm)


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