netdev - Re: [PATCH net] rhashtable: use cond

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Message-ID: <20150226154643.GA18965@acer.localdomain>
Date:	Thu, 26 Feb 2015 15:46:44 +0000
From:	Patrick McHardy <kaber@...sh.net>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	'Eric Dumazet' <eric.dumazet@...il.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"tgraf@...g.ch" <tgraf@...g.ch>,
	"pablo@...filter.org" <pablo@...filter.org>,
	"johunt@...mai.com" <johunt@...mai.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] rhashtable: use cond_resched()

On 26.02, David Laight wrote:
> From: Eric Dumazet 
> Sent: 26 February 2015 15:21
> > If a hash table has 128 slots and 16384 elems, expand to 256 slots
> > takes more than one second. For larger sets, a soft lockup is detected.
> 
> What on earth is it doing?
> Presumably something to do with the rcu actions needed to allow
> lockless lookup during resize.
> 
> There has to be a better solution?
> Perhaps even two sets of chain pointers down the hash lists.
> Then the old hash table can be kept completely valid while the
> whole 'unzip' action is done.

One of the main points of rhashtable is that you don't need those.
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