On 31/01/14 18:56, Wei Liu wrote: > On Thu, Jan 30, 2014 at 07:08:11PM +0000, Zoltan Kiss wrote: >> Hi, >> >> I've experienced some queue timeout problems mentioned in the >> subject with igb and bnx2 cards. I haven't seen them on other cards >> so far. I'm using XenServer with 3.10 Dom0 kernel (however igb were >> already updated to latest version), and there are Windows guests >> sending data through these cards. I noticed these problems in XenRT >> test runs, and I know that they usually mean some lost interrupt >> problem or other hardware error, but in my case they started to >> appear more often, and they are likely connected to my netback grant >> mapping patches. These patches causing skb's with huge (~64kb) >> linear buffers to appear more often. >> The reason for that is an old problem in the ring protocol: >> originally the maximum amount of slots were linked to MAX_SKB_FRAGS, >> as every slot ended up as a frag of the skb. When this value were >> changed, netback had to cope with the situation by coalescing the >> packets into fewer frags. >> My patch series take a different approach: the leftover slots >> (pages) were assigned to a new skb's frags, and that skb were >> stashed to the frag_list of the first one. Then, before sending it >> off to the stack it calls skb = skb_copy_expand(skb, 0, 0, >> GFP_ATOMIC, __GFP_NOWARN), which basically creates a new skb and >> copied all the data into it. As far as I understood, it put >> everything into the linear buffer, which can amount to 64KB at most. >> The original skb are freed then, and this new one were sent to the >> stack. > > Just my two cents, if it is this case, you can try to call > skb_copy_expand on every SKB netback receives to manually create SKBs > with ~64KB linear buffer to see how it goes...
I've tried it, and it did break everything in a similar way, so that's a strong clue that the problem lies here. I've rewrote that part of my patches to do less modification, based on Malcolm's idea: netback pulls the first frag into linear buffer, then moves a frag from the frag_list skb into the first one. That seems to help, but so far I have only one relevant test result, I'm waiting for more results. Zoli ------------------------------------------------------------------------------ Managing the Performance of Cloud-Based Applications Take advantage of what the Cloud has to offer - Avoid Common Pitfalls. Read the Whitepaper. http://pubads.g.doubleclick.net/gampad/clk?id=121051231&iu=/4140/ostg.clktrk _______________________________________________ E1000-devel mailing list E1000-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/e1000-devel To learn more about Intel® Ethernet, visit http://communities.intel.com/community/wired
