netdev - RE: [PATCH net-next] tcp: shrink tcp6_timewait

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B736F@saturn3.aculab.com>
Date:	Wed, 2 Oct 2013 13:08:20 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"David Miller" <davem@...emloft.net>
Cc:	"netdev" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next] tcp: shrink tcp6_timewait_sock by one cache line

> -	tmo = tw->tw_ttd - jiffies;
> +	tmo = tw->tw_ttd - (u32)jiffies;

Do you need any of these (u32) casts?
The compiler will almost certainly use 32bit arithmetic (on 32bit systems at least)
because the 'as if' rule lets if use the smaller type.

> +		tw->tw_ttd = (u32)(jiffies + (slot << INET_TWDR_RECYCLE_TICK));

If that (u32) cast is needed in order to avoid 64bit maths, it is in the wrong place.

	David