netdev - Re: Ottawa and slow hash-table resize

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Date:	Mon, 23 Feb 2015 21:03:58 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	josh@...htriplett.org
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	alexei.starovoitov@...il.com, herbert@...dor.apana.org.au,
	kaber@...sh.net, davem@...emloft.net, ying.xue@...driver.com,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: Ottawa and slow hash-table resize

On 02/23/15 at 11:12am, josh@...htriplett.org wrote:
> In theory, resizes should only take the locks for the buckets they're
> currently unzipping, and adds should take those same locks.  Neither one
> should take a whole-table lock, other than resize excluding concurrent
> resizes.  Is that still insufficient?

Correct, this is what happens. The problem is basically that
if we insert from atomic context we cannot slow down inserts
and the table may not grow quickly enough.

> Yeah, the add/remove statistics used for tracking would need some
> special handling to avoid being a table-wide bottleneck.

Daniel is working on a patch to do per-cpu element counting
with a batched update cycle.
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