On Wed, Jul 31, 2013 at 3:15 AM, Yijing Wang <wangyijing@xxxxxxxxxx> wrote: > Hi Bjorn, > I didn't observe a performance difference between MPS=128 and MPS=512. I use ping $dest_ip -s 65500(large size packet) > to test the different situations. Interesting. "ping" is probably not a good way to see performance differences, but hopefully you could see a difference in *some* scenario. Otherwise, there's not much point in increasing MPS :) >> I assume there are no AER or other errors logged by the root port? > Yes, AER is not support in local machine. Per the 5520/5500 spec, it does support AER (sec 19.11.5). Maybe there's some platform support required in addition. You might still be able to see some info just with "lspci -vv" > Hmmm, PCIe Spec does not involve too much about MPS setting. So maybe different platform > has different strategy. I think there's enough in the spec to tell us what we need to do (this is sec 2.2.2): - A Transmitter must not send a TLP larger than its Max_Payload_Size - A Receiver must treat TLPs larger than its Max_Payload_Size as malformed The only way I can see to guarantee that is to set the MPS on both ends of the link the same. > Conservatively, as a improvement for mps setting after hotplug. I think update mps setting equal to its parent > make sense. This is no harm to other devices, we only modify the hotplug device itself mps register. > > So if you agree, I will update my patch ,only try to modify hotplug device mps, make them equal to its parent. Yes, I think that would be safe. If the switch is set to a larger MPS than the hot-added device supports, I don't think we can safely use the device. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
