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Date: Thu, 21 Aug 2014 21:25:14 -0700 (PDT) From: David Miller <davem@...emloft.net> To: bpoirier@...e.de Cc: mchan@...adcom.com, prashant@...adcom.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/3] tg3: Fix tx_pending checks for tg3_tso_bug From: Benjamin Poirier <bpoirier@...e.de> Date: Thu, 21 Aug 2014 14:59:11 -0700 > Ah, now I understand the reason for the * 3 in > u32 frag_cnt_est = skb_shinfo(skb)->gso_segs * 3; > > /* Estimate the number of fragments in the worst case */ > but that is not really the "worst case". It's not forbidden to have more than > two frags per skb output from skb_gso_segment(). I've kept this estimation > approach but I've added code to validate the estimation or else linearize the > skb. This is a common situation drivers run into, and there have been a few notable situations in virtualization drivers recently. Although in those cases the problems arise from the fact that if an SKB fragment is a compound page, this can evaluate to requiring multiple descriptors, one for each 4K segment within that fragment. Anyways, the point I wanted to make is that you shouldn't do anything too complicated to handle all of this. And I think your conclusion to linearize if the estimation fails is a good one. -- 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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