[Winpcap-users] packet lost at 480Mbps

[Guy Harris]

On Mar 16, 2009, at 9:00 AM, Gianluca Varenni wrote:

> Yeah. Actually "Receive buffer space" is a generic term. Most  
> probably the DMA receive buffers (that are in the RAM of your PC)  
> are not big enough,

...which would require that the driver be changed (difficult to do  
without source; you'd have to ask whoever wrote the driver, probably  
the NIC supplier) or that some parameter of the driver be changed to  
allocate a bigger receive buffer (you'd have to ask whoever write the  
driver whether there is such a parameter and how to change it).

> or the PCI/PCIe/USB bus on which the NIC is installed is not fast  
> enough to transfer all the data from the device to the host.

..which might require that you get a machine with a higher-bandwidth  
bus or memory subsystem (or multiple buses, or...).

> Decreasing the mintocopy can actually impact the perfomance in the  
> opposite way: if mintocopy is low, the number of user/ 
> kerneltransitions (i.e. system calls) to move packets from kernel  
> mode to user mode gets higher and can impact the CPU load on the  
> system.

I.e., decreasing mintocopy might improve latency (the application  
would see packets sooner after they're received) but reduce throughput  
(more overhead per packet, so possibly fewer packets/second that can  
be handled).