netdev - Re: [PATCH 05/15] RDS: increase size of hash-table to 8K

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Message-Id: <20150921.160527.1218605543469993281.davem@davemloft.net>
Date:	Mon, 21 Sep 2015 16:05:27 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	santosh.shilimkar@...cle.com
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	ssantosh@...nel.org
Subject: Re: [PATCH 05/15] RDS: increase size of hash-table to 8K

From: Santosh Shilimkar <santosh.shilimkar@...cle.com>
Date: Sat, 19 Sep 2015 19:04:42 -0400

> Even with per bucket locking scheme, in a massive parallel
> system with active rds sockets which could be in excess of multiple
> of 10K, rds_bin_lookup() workload is siginificant because of smaller
> hashtable size.
> 
> With some tests, it was found that we get modest but still nice
> reduction in rds_bind_lookup with bigger bucket.
> 
> 	Hashtable	Baseline(1k)	Delta
> 	2048:		8.28%     	-2.45%
> 	4096:		8.28%		-4.60%
> 	8192:		8.28%		-6.46%
> 	16384:		8.28%		-6.75%
> 
> Based on the data, we set 8K as the bind hash-table size.
> 
> Signed-off-by: Santosh Shilimkar <ssantosh@...nel.org>
> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@...cle.com>

Like others I would strongly prefer that you use a dynamically sized
hash table.

Eating 8k just because a module just happened to get loaded is really
not appropriate.

And there are many other places that use such a scheme, one example is
the AF_NETLINK socket hash table.
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