From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster
Date: Sat, 24 Oct 2009 16:24:27 +0200
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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> <20091024135214.GB6638@linux.vnet.ibm.com>
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Cc: Octavian Purdila <opurdila@ixiacom.com>,
	Benjamin LaHaise <bcrl@lhnet.ca>, netdev@vger.kernel.org,
	Cosmin Ratiu <cratiu@ixiacom.com>
To: paulmck@linux.vnet.ibm.com
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Paul E. McKenney a =E9crit :
> On Sat, Oct 24, 2009 at 10:49:55AM +0200, Eric Dumazet wrote:
>>
>> On my dev machine, a synchronize_rcu() lasts between 2 an 12 ms
>=20
> That sounds like the right range, depending on what else is happening
> on the machine at the time.
>=20
> 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.
>=20

Hmm... I'll make some experiments Monday and post results, but it seems=
 very
promising.

Do you think the "on_each_cpu(flush_backlog, dev, 1);"
we perform right before calling netdev_wait_allrefs() could be changed
somehow to speedup rcu callbacks ? Maybe we ould avoid sending IPI twic=
e to
cpus ?

Thanks