libluatsc

Lua 5.5 library to read 64-bit time-stamp counter and TSC_AUX value.

The TSC register can be used by performance-analysis applications, along with the performance monitoring registers, to help determine the relative frequency of an event or its duration. TSC is incremented at a rate corresponding to the baseline frequency of the processor (which may differ from actual processor frequency in low power modes of operation).

Supports SSE 2 and if available will, by default:

1. be executed only after all previous stores are globally visible; and
2. be executed prior to execution of any subsequent instruction (including any memory accesses).

Usage

Binaries for AMD64 are available on Releases page. For x86, build with build.sh script. If on Windows, use MinGW/MSYS2 with CFLAGS and LFLAGS set to include and library paths, respectively.

env CFLAGS=-IC:/msys64/usr/local/include \
    LFLAGS=-LC:/msys64/usr/local/bin ./build.sh

NOTE: If you want to use MSVC, you are on your own, sorry.

Then, require and call now() to get the counter and TSC_AUX. On most systems, TSC_AUX is initialized by privileged software with a signature value (e.g., a logical processor ID).

local tsc = require("libluatsc")

local stamp, aux = tsc.now()
print("stamp:", stamp, "aux:", aux)

--[[
  The time stamp counter in newer processors may
  support an enhancement, referred to as invariant TSC ]]--
print("is invariant?", tsc.isinvariant())

...might output:

stamp:  50806050955569   aux:   6
is invariant?   true

NOTE: If the Lua code above fails with module 'libluatsc' not found on Windows, add package.cpath=".\\?.dll" one line before require or change your LUA_CPATH environment variable to include .\\?.dll.

Calculating delta time

To find the difference in seconds between two time stamps, you'll need to divide the result of T_end minus T_begin by the the processor clock speed.

local tsc = require("libluatsc")
-- from: https://github.com/oAGoulart/libluacrc32
local crc32 = require("libluacrc32")

local inp = assert(io.open("1MB.png", "rb"))
local data = inp:read("*all")
local dlen = string.len(data)
inp:close()

local begin, baux = tsc.now()
local res = crc32.calculate(data, "ISCSI")
local endin, eaux = tsc.now()

os.execute("grep -m1 \"cpu MHz\" /proc/cpuinfo >> .cpuspd")
local cs = assert(io.open(".cpuspd", "r"))
local result = cs:read("*a")
cs:close()
local cpuspd = tonumber(result:match("%d+.%d+"))

local deltat = (endin - begin) / cpuspd
print("delta time:", deltat, "μs", -- (MHz = 1e+6 = microsecond)
      "\ndata length:", dlen, "bytes",
      "\nthroughput:", dlen / deltat, "MB/s")

...might output:

delta time:     200.21097287982 μs
data length:    1066752 bytes
throughput:     5328.1395352907 MB/s