netdev - Re: tbench regression in 2.6.25-rc1

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Date:	Mon, 18 Feb 2008 12:33:53 -0500
From:	Valdis.Kletnieks@...edu
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	David Miller <davem@...emloft.net>, dada1@...mosbay.com,
	herbert@...dor.apana.org.au, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: tbench regression in 2.6.25-rc1

On Mon, 18 Feb 2008 16:12:38 +0800, "Zhang, Yanmin" said:

> I also think __refcnt is the key. I did a new testing by adding 2 unsigned long
> pading before lastuse, so the 3 members are moved to next cache line. The performance is
> recovered.
> 
> How about below patch? Almost all performance is recovered with the new patch.
> 
> Signed-off-by: Zhang Yanmin <yanmin.zhang@...el.com>

Could you add a comment someplace that says "refcnt wants to be on a different
cache line from input/output/ops or performance tanks badly", to warn some
future kernel hacker who starts adding new fields to the structure?

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