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Date: Tue, 20 Aug 2013 18:24:57 +0200 From: Johannes Berg <johannes@...solutions.net> To: Stephen Hemminger <stephen@...workplumber.org> Cc: Florian Fainelli <f.fainelli@...il.com>, Eric Dumazet <eric.dumazet@...il.com>, Ben Hutchings <bhutchings@...arflare.com>, netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org Subject: Re: changing dev->needed_headroom/needed_tailroom? On Tue, 2013-08-20 at 09:20 -0700, Stephen Hemminger wrote: > All code must check for needed headroom first, and copy packet > if space is not available. Since excess headroom is always safe, > most devices just always use the same worst case headroom. > > Even with your changes this will still be necessary since packets will > be still in flight while features change. I agree, it will always be necessary. I guess the question boils down to whether/what N bytes headroom more or less actually make a difference. The wireless stack currently sets needed_headroom to 34 or so I think, but I will need to increase by 8 which was why I had this question to start with. However, those 34 are an absolute worst case - in most cases it's much less... So I suppose the other question we should ask is will increasing from ~34 to ~42 make a significant different that it's worth thinking about avoiding it in the common cases at all? johannes -- 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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