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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B707F@saturn3.aculab.com> Date: Wed, 31 Oct 2012 08:57:43 -0000 From: "David Laight" <David.Laight@...LAB.COM> To: HÃ¥vard Skinnemoen <havard@...nnemoen.net> 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. It's a ring buffer (I presume) the pointers can be in either order. David -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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