以下 MWE 在几种情况下编译（删除了相应的行）给出了以下时间安排（运行期间删除了所有输出文件），如Measure-Command在 Windows 7 Powershell 上使用 TL2014 计时：
Engine | unicode-math? | sisetup options | Time
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lualatex | unicode-math | per-mode=symbol-or-fraction | ~53 sec
lualatex | unicode-math | per-mode=default | ~5 sec
lualatex | no unicode-math | per-mode=symbol-or-fraction | ~2 sec
lualatex | fontspec | per-mode=symbol-or-fraction | ~4 sec
xelatex | unicode-math | per-mode=symbol-or-fraction | ~4 sec
xelatex | no unicode-math | per-mode=symbol-or-fraction | ~2 sec
pdflatex | no unicode-math | per-mode=default | ~1 sec
pdflatex | no unicode-math | per-mode=symbol-or-fraction | ~1 sec
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为什么添加per-mode=symbol-or-fractionwithunicode-math会使编译时间增加一个数量级lualatex？
二进制版本：
LuaTeX, Version beta-0.79.1 (rev 4971)
XeTeX 3.14159265-2.6-0.99991
pdfTeX 3.14159265-2.6-1.40.15
\documentclass{article}
\usepackage{mathtools}
\usepackage{unicode-math}
\usepackage{siunitx}
\sisetup{
per-mode = symbol-or-fraction,
}
\begin{document}
\begin{align*}
\text{at $p=\SI{1.0}{\MPa}$:}\begin{cases}
v(T) &= v_1 + \left(T - T_1\right)\frac{v_2 - v_1}{T_2 - T_1} \\
v(\SI{220}{\degreeCelsius}) &= \SI{0.2060}{\meter\cubed\per\kilogram} + \left(\SI{220}{\degreeCelsius} - \SI{200}{\degreeCelsius}\right) \frac{\SI{0.2275}{\meter\cubed\per\kilogram} - \SI{0.2060}{\meter\cubed\per\kilogram}}{\SI{240}{\degreeCelsius} - \SI{200}{\degreeCelsius}} \\
v(\SI{220}{\degreeCelsius}) &= \SI{0.21675}{\meter\cubed\per\kilogram}
\end{cases}\\
\text{at $p=\SI{1.5}{\MPa}$:}\begin{cases}
v(T) &= v_1 + \left(T - T_1\right)\frac{v_2 - v_1}{T_2 - T_1} \\
v(\SI{220}{\degreeCelsius}) &= \SI{0.1325}{\meter\cubed\per\kilogram} + \left(\SI{220}{\degreeCelsius} - \SI{200}{\degreeCelsius}\right) \frac{\SI{0.1483}{\meter\cubed\per\kilogram} - \SI{0.1325}{\meter\cubed\per\kilogram}}{\SI{240}{\degreeCelsius} - \SI{200}{\degreeCelsius}} \\
v(\SI{220}{\degreeCelsius}) &= \SI{0.1404}{\meter\cubed\per\kilogram}
\end{cases}\\
\text{at $T=\SI{220}{\degreeCelsius}$:}\begin{cases}
v(p) &= v_1 + \left(p - p_1\right)\frac{v_2 - v_1}{p_2 - p_1} \\
v(\SI{1.4}{\MPa}) &= \SI{0.21675}{\meter\cubed\per\kilogram} + \left(\SI{1.4}{\MPa} - \SI{1.0}{\MPa}\right) \frac{\SI{0.1404}{\meter\cubed\per\kilogram} - \SI{0.21675}{\meter\cubed\per\kilogram}}{\SI{1.5}{\MPa} - \SI{1.0}{\MPa}} \\
v(\SI{1.4}{\MPa}) &= \SI{0.1557}{\meter\cubed\per\kilogram}
\end{cases}
\end{align*}
\end{document}