linux-kernel - Re: [PATCH v3 06/10] net/macb: clean up ring buffer logic

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Message-ID: <CACiLriQnQcoXFqrqNt3nkY47nR8FnXbqWjtPRp250gueHSMDmQ@mail.gmail.com>
Date:	Tue, 30 Oct 2012 11:22:51 -0700
From:	Håvard Skinnemoen <havard@...nnemoen.net>
To:	David Laight <David.Laight@...lab.com>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>, netdev@...r.kernel.org,
	davem@...emloft.net, bhutchings@...arflare.com,
	linux-arm-kernel@...ts.infradead.org, plagnioj@...osoft.com,
	patrice.vilchez@...el.com, linux-kernel@...r.kernel.org,
	manabian@...il.com
Subject: Re: [PATCH v3 06/10] net/macb: clean up ring buffer logic

On Tue, Oct 30, 2012 at 4:12 AM, David Laight <David.Laight@...lab.com> wrote:
>> Instead of masking head and tail every time we increment them, just let them
>> wrap through UINT_MAX and mask them when subscripting. Add simple accessor
>> functions to do the subscripting properly to minimize the chances of messing
>> this up.
> ...
>> +static unsigned int macb_tx_ring_avail(struct macb *bp)
>> +{
>> +     return TX_RING_SIZE - (bp->tx_head - bp->tx_tail);
>> +}
>
> That one doesn't look quite right to me.
> Surely it should be masking with 'TX_RING_SIZE - 1'

Why is that? head and tail can never be more than TX_RING_SIZE apart,
so it shouldn't make any difference.

Havard
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