Performance difference Foundation JSON vs. PureSwiftJSON

[fabianfett]

swift 5.1.4 on Amazon Linux 2

Foundation.JSONCoding
-----------------------------
string, cold: 25724953 (ns)
string, warm: 370171 (ns)
json, cold: 25843952 (ns)
json, warm: 423885 (ns)
-----------------------------

PureSwiftJSONCoding
-----------------------------
string, cold: 23219984 (ns)
string, warm: 372525 (ns)
json, cold: 23525811 (ns)
json, warm: 390062 (ns)
-----------------------------

boot speedup: 8-10% (not linking Foundation, statically linking PureSwiftJSONCoding)
json warm speedup: 8% should be more with larger json payloads.

[fabianfett]

Difference in linked Frameworks:

With Foundation
bash-4.2# ldd .build/release/SwiftAwsLambdaSample
	linux-vdso.so.1 (0x00007fff38d64000)
	libswiftGlibc.so => /usr/lib/swift/linux/libswiftGlibc.so (0x00007f0cedcfe000)
	libswiftCore.so => /usr/lib/swift/linux/libswiftCore.so (0x00007f0ced2f6000)
	libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f0ced0d8000)
	libutil.so.1 => /lib64/libutil.so.1 (0x00007f0ceced5000)
	libdl.so.2 => /lib64/libdl.so.2 (0x00007f0ceccd1000)
	libm.so.6 => /lib64/libm.so.6 (0x00007f0cec991000)
	libswiftDispatch.so => /usr/lib/swift/linux/libswiftDispatch.so (0x00007f0cedcc3000)
	libdispatch.so => /usr/lib/swift/linux/libdispatch.so (0x00007f0cedc61000)
	libBlocksRuntime.so => /usr/lib/swift/linux/libBlocksRuntime.so (0x00007f0cec78e000)
	libFoundation.so => /usr/lib/swift/linux/libFoundation.so (0x00007f0cebf12000)
	libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f0cebb90000)
	libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f0ceb97a000)
	libc.so.6 => /lib64/libc.so.6 (0x00007f0ceb5cf000)
	libatomic.so.1 => /lib64/libatomic.so.1 (0x00007f0ceb3c7000)
	libicui18nswift.so.61 => /usr/lib/swift/linux/libicui18nswift.so.61 (0x00007f0ceaed3000)
	libicuucswift.so.61 => /usr/lib/swift/linux/libicuucswift.so.61 (0x00007f0ceaaed000)
	libicudataswift.so.61 => /usr/lib/swift/linux/libicudataswift.so.61 (0x00007f0ce8f48000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f0cedaed000)
	librt.so.1 => /lib64/librt.so.1 (0x00007f0ce8d40000)

Without Foundation
bash-4.2# ldd .build/release/SwiftAwsLambdaSample
	linux-vdso.so.1 (0x00007ffde178a000)
	libswiftGlibc.so => /usr/lib/swift/linux/libswiftGlibc.so (0x00007f1e6bccb000)
	libswiftCore.so => /usr/lib/swift/linux/libswiftCore.so (0x00007f1e6b2c3000)
	libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f1e6b0a5000)
	libutil.so.1 => /lib64/libutil.so.1 (0x00007f1e6aea2000)
	libdl.so.2 => /lib64/libdl.so.2 (0x00007f1e6ac9e000)
	libm.so.6 => /lib64/libm.so.6 (0x00007f1e6a95e000)
	libswiftDispatch.so => /usr/lib/swift/linux/libswiftDispatch.so (0x00007f1e6bc90000)
	libdispatch.so => /usr/lib/swift/linux/libdispatch.so (0x00007f1e6bc2e000)
	libBlocksRuntime.so => /usr/lib/swift/linux/libBlocksRuntime.so (0x00007f1e6a75b000)
	libFoundation.so => /usr/lib/swift/linux/libFoundation.so (0x00007f1e69edf000)
	libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f1e69b5d000)
	libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f1e69947000)
	libc.so.6 => /lib64/libc.so.6 (0x00007f1e6959c000)
	libatomic.so.1 => /lib64/libatomic.so.1 (0x00007f1e69394000)
	libicui18nswift.so.61 => /usr/lib/swift/linux/libicui18nswift.so.61 (0x00007f1e68ea0000)
	libicuucswift.so.61 => /usr/lib/swift/linux/libicuucswift.so.61 (0x00007f1e68aba000)
	libicudataswift.so.61 => /usr/lib/swift/linux/libicudataswift.so.61 (0x00007f1e66f15000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f1e6baba000)
	librt.so.1 => /lib64/librt.so.1 (0x00007f1e66d0d000)

It really is just on Framework difference. Foundation does not require more frameworks (than needed anyways) to be linked.