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Date: Mon, 12 May 2008 15:58:58 -0700 From: "Jerry Chu" <hkchu@...gle.com> To: "David Miller" <davem@...emloft.net> Cc: netdev@...r.kernel.org Subject: Re: Socket buffer sizes with autotuning On Mon, May 12, 2008 at 3:29 PM, David Miller <davem@...emloft.net> wrote: > From: "Jerry Chu" <hkchu@...gle.com> > Date: Mon, 12 May 2008 15:22:55 -0700 > > > > I did a quick prototype based on your idea of adding an "in_flight" > > field to skb_shared_info to track how many in-flight clones in the > > host. I tested > > it quickly and it doesn't work. After some thought it was obvious why it > > won't work. It's because what the TCP stack needs is to track how > > many in-flight pkts are in the host, but your proposed patch increments > > "in_flight" once on the 1st __skb_clone() to be sent to the driver, but > > decrements "in_flight" TWICE, one for each of the clones to be freed. > > I did a quick hack to make it work for my limited test case but I haven't > > figured out an acceptable (non-hack) solution. > > That's easy to fix, only set the in_flight pointer in the child clone > skb. Thanks for figuring that out. I must be missing something. All the clones share the same "skb_shared_info", how does one only set in_flight in one clone but not the other? > > > > Continued testing, I discovered the problem I described below where > > "in_flight" may point to a tp that has already been freed can not be > > addressed by zapping skb_shinfo(skb)->in_flight in sock_wfree(). The > > reason is that pkts may be acked and freed by TCP before driver freeing > > up its clone copy (e.g., due to driver lazy reclaim...) When that happens > > the "host_inflight" accounting will get messed up. > > Simply notice, when we're about to decrement in_flight, that the data > reference is one. You can take appropriate actions if so. > Jerry -- 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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