Hello, I have released simple-sendfile v0.2.4. In short, this version is 100+ times faster than v0.2.3 in some cases. I always did benchmark mighttpd with high concurrency. That is, I always make multiple connections at the same time. It gives me a good result. However, when I set the number of concurrency to 1, I found mighttpd is unbearablely slow on Linux and FreeBSD. I realized that this is because that warp uses sendMany (the writev() syscall) for a header and sendfile (the sendfile () syscall) for a body (ie. a file). They are sent in separate TCP packets. simple-sendfile v0.2.4 provides a new function called sendfileWithHeader. On Linux, it uses the send() syscall with the MSG_MORE flag to *store* a header and the sendfile() syscall to send both the stored header and a file. On FreeBSD, it uses the sendfile() syscall with the header arguments to send both a header and a file. This trick ensures that both a header and a body is sent in a single TCP packet. On Mac, v0.2.3 sends separate packets but is fast. I don't know why. v0.2.4 uses the same logic of FreeBSD. Unfortunately, the header and the body is also sent separately but it is still fast. Again, I don't know why. Here is the result of benchmark: OLD+pronk NEW+pronk OLD+httperf NEW+httperf Mac 3678.74 3415.76 6642.5 6891.8 FreeBSD 10.0010 1309.43 10.0 3174.8 # this machine is slow Linux 24.9875 2558.36 25.0 8284.2 OLD means v0.2.3. NEW means v0.2.4. pronk is "pronk -c 1 -n 1000 -r 10000 -b http://127.0.0.1:8000/" httperf is "httperf --hog --num-conns 1 --num-calls 1000 --rate 10000 --server localhost --port 8000 --uri /" I have already sent a pull request to warp to use sendfileWithHeader: https://github.com/yesodweb/wai/pull/86 P.S. I also found that the network package cannot find IPV6_V6ONLY macro on FreeBSD because the test code does not include "netinet/in.h". I will sent a pull request to fix this later. --Kazu