# Aleksey Kladov - It’s Not Always iCache (Highlights)  ## Highlights - On Linux, the best tool to quickly access the performance of any program is perf stat. #performance #example #linux code ``` $ perf stat -e instructions,cycles,\ L1-dcache-loads,L1-dcache-load-misses,L1-dcache-prefetches,\ L1-icache-loads,L1-icache-load-misses,cache-misses \ ./always ``` ` - While perf takes the real data from the CPU, an alternative approach is to run the program in a simulated environment. That’s what cachegrind tool does. - Note that the number of times CPU refers to iCache should correspond to the number of instructions it executes. ### Conclusions - Inlining might cause C to use more registers. This means that prologue and epilogue grow additional push/pop instructions, which also use stack memory. - Generalizing from the first point, if S is called in a loop or in an if, the compiler might hoist some instructions of S to before the branch, moving them from the cold path to the hot path. - With more local variables and control flow in the stack frame to juggle, compiler might accidentally pessimize the hot loop.