![]() The TCP segmenting work is done by the network adapter/driver hardware instead of the host CPU. This allows TCP to allocate a buffer of up to 64K to the driver, which divides the large buffer into packets that fit within the network MTU. Windows offers the ability for the network adapter/driver to advertise a larger Maximum Segment Size (MSS) than the MTU to TCP up to 64K. On systems where the CPU is not necessarily busy, such as a client system, the benefit of offloading checksum may be seen in better network response times, rather than in noticeably improved throughput. Increased benefit can be seen on systems that act as both client and server, such as a sockets proxy server. Offloading checksum on the receiver has the same advantages as offloading checksum on the sender. Analysis of this improvement shows that 11% of the total improvement is due to the path length reduction, and 8% is due to increasing the caches effectiveness. In the Windows Performance Lab, we have measured TCP throughput improvements of 19% when checksum was offloaded during network-intensive workloads. Offloading checksum calculation to the sender improves the overall system performance by reducing the load on the host CPU and increasing cache effectiveness. It causes cache churning effects (typically on the sender).Checksum calculation is the most expensive function in the networking stack for two reasons: These are particularly important for the high-end network adapter that will be used in configurations requiring top performance.įor most common network traffic, offloading checksum calculation to the network adapter hardware offers a significant performance advantage by reducing the number of CPU cycles required per byte. It is becoming increasingly important to consider adding task offload features that allow for interrupt moderation, dynamic tuning on the hardware, improving the use of the PCI bus, and supporting Jumbo Frames. There are always tradeoffs in deciding which hardware functions to implement on a network adapter.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |