netdev - Re: [PATCH] enic: fix adaptive irq coalescing on 32-bit

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Date:	Fri, 23 May 2014 11:29:15 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	David Laight <David.Laight@...lab.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Sujith Sankar <ssujith@...co.com>,
	Neel Patel <neepatel@...co.com>,
	Govindarajulu Varadarajan <_govind@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Christian Benvenuti <benve@...co.com>
Subject: Re: [PATCH] enic: fix adaptive irq coalescing on 32-bit

On Friday 23 May 2014 08:29:52 David Laight wrote:
> From: Arnd Bergmann
> > 7c2ce6e60f703 "enic: Add support for adaptive interrupt coalescing"
> > introduced a 64-bit division that causes a link error on all 32-bit
> > machines:
> > 
> > drivers/built-in.o: In function `enic_poll_msix':
> > :(.text+0x54ff00): undefined reference to `__aeabi_uldivmod'
> > 
> > Since we are dividing another 32-bit value and are only interested
> > in the approximate range here, it should always be safe to limit
> > the delta to an u32 value.
> ...
> >  	traffic <<= 3;
> > -	traffic /= delta;
> > +	traffic /= min_t(u32, delta, UINT_MAX);
> 
> I suspect that doesn't have the desired effect.
> I think it is the same as:
> 	traffic /= (u32)delta;

Ah, you are right, sorry for that.

> If you was the correct value for large 'delta' then maybe:
> 	traffic = delta > UINT_MAX ? 0 : traffic / (u32)delta;

That looks better, yes.

	Arnd
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