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Date: Mon, 17 Nov 2014 08:45:17 -0800 From: Eric Dumazet <eric.dumazet@...il.com> To: "Nelson, Shannon" <shannon.nelson@...el.com> Cc: "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>, "davem@...emloft.net" <davem@...emloft.net>, "Kong, Serey" <serey.kong@...el.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "nhorman@...hat.com" <nhorman@...hat.com>, "sassmann@...hat.com" <sassmann@...hat.com>, "jogreene@...hat.com" <jogreene@...hat.com> Subject: Re: [net-next 03/12] i40e: Handle a single mss packet with more than 8 frags On Mon, 2014-11-17 at 16:04 +0000, Nelson, Shannon wrote: > This typically hits when there are many little TSO packets in a single > MTU size frame. The hardware doesn't like dealing with more than 8 > separate buffers. > > If skb_linearize() fails and we try to send the skb as is, the > hardware will throw an MDD event and disable that particular queue, > possibly causing a Tx hang, which will lead to a PF reset and then we > continue on. It's a bit of a hit to throughput, and most folks get a > little annoyed when seeing the Tx hang stack trace in their log, but > it generally isn't fatal. > > If we disable the MDD detection, the hardware ends up putting garbage > on the wire. > > It looks to me that the way for skb_linearize() to fail is with > -ENOMEM, in which case we probably have other issues. > This kind of events happens in real workloads, trust me. > If there are some alternative suggestions for dealing with this, we'd > be happy to hear about them. Nelson, all you have to do is to check skb_linearize(skb) return code. If its a failure, then drop this packet. How hard is this ? This should hardly trigger in normal conditions. If some customer complains, then you might implement something more complex in the future. Lets fix the bug first in a 100% safe way. -- 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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