netdev - Re: [PATCH 0/1] Rosebush, a new hash table

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Message-ID: <ZdrV3+kNz/ez4iai@gondor.apana.org.au>
Date: Sun, 25 Feb 2024 13:53:35 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Matthew Wilcox <willy@...radead.org>,
	David Laight <David.Laight@...lab.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Graf <tgraf@...g.ch>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
	"rcu@...r.kernel.org" <rcu@...r.kernel.org>
Subject: Re: [PATCH 0/1] Rosebush, a new hash table

On Sun, Feb 25, 2024 at 12:51:06AM -0500, Kent Overstreet wrote:
>
> but your distribution actually is accurate in general, golden ratio hash
> is relly nice for sequential integers. the actual problem with your test
> is that you're testing 100% occupancy - no one does that.
> 
> 75% occupancy, siphash:
> 0: 933
> 1: 60
> 2: 6
> 3: 1
> 4: 0
> 
> that looks about right to me.

The point is that the worst-case length grows with the size of
the table so it won't always be 3.  You need to take into account
the largest table size that you will support.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt