improving loopback throughput

Question

While working on improving performance of an application which requires to do socket IPC bounded to localhost, came across following article :
https://learn.microsoft.com/en-us/windows-hardware/drivers/network/sio-loopback-fast-path

Setting "SIO_LOOPBACK_FAST_PATH" does improve throughput and explanation in the document does sound logical as well.

However, what got me worrying about usage of "SIO_LOOPBACK_FAST_PATH" is that article mentions this ioctl as deprecated.

So, here's the question; are there any alternatives to "SIO_LOOPBACK_FAST_PATH" ioctl? If so, could you please point me to it.

Answer 1

It's marked as "deprecated" for a few reasons:

• In recent OS versions, the normal, non-fast-path loopback has been improved quite a bit, such that SIO_LOOPBACK_FAST_PATH doesn't give as much benefit anymore.
• The option doesn't coexist with all other socket options, so there are some gotchas lurking there
• Not all WFP callout drivers support this option, so it may not interop well with other 3rd party software

We continue to work to make the loopback path fast, and the hope is that we can eventually make this socket option a no-op, since eventually the normal path will be just as fast as the "fast path".

All that being said, if you do measure a valuable perf benefit to using this flag (especially on older versions of the OS), you may certainly use it.