RE: PacketSendPackets and latency

Hi,

 

So the delay increases with the size of buffer in a linear fashion, the packets send with the correct delays between them what we get is a big “hole” in sending between chunks of packets.

 

As far as I can see direction mode is used which should mean no copies to a  buffer for transfers to the driver should be done which is what seems to be the most likely cause of the delay.

 

I have not evaluated if we see the same issue on reads from the driver but will probably aim to do so.

 

David

 

 

From: Varunram Ganesh [mailto:[email protected]] 
Sent: Thursday, March 23, 2017 9:10 AM
To: Nmap-dev
Cc: Daniel Miller; David Atkins
Subject: Re: PacketSendPackets and latency

 

Hi David,

 

Disregard what I said about -d2. I thought you were trying to send data using --send-eth and similar using nmap.

 

Coming back to the problem at hand, from what I know with regard to npf, NPF_BufferedWrite() scans the buffer and then calls NdisSend to send the same. So, if the buffer has enough space, it should queue the data, send and immediately return. I have seen such errors only when we receive and send packets both at the same time, but I haven't sent 30Mb or seen issues which report the same. A quick question - Does Sending a smaller buffer cause the same 13ms delays? My guess is that its taking time to scan the buffer (assuming you are resetting the buffer contents), but I could be wrong.

 

 

Cheers,

 

Varunram

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