Windows 10 is faster with -fno-openmp than setDTthreads(1) on many repeated calls #4527
Description
OpenMP support may cause issues with Windows performance, especially with many repeated calls.
library(data.table)
setDTthreads(1L)
allIterations <- data.table(v1 = runif(1e5), v2 = runif(1e5))
DoSomething <- function(row) someCalculation <- row[["v1"]] + 1
system.time(for (r in 1:nrow(allIterations)) DoSomething(allIterations[r, ]))
##1.12.8
## user system elapsed
## 17.09 4.48 22.14
##master
## user system elapsed
## 17.50 4.53 22.51
##master w/ OpenMP lines deleted from subset.c
## user system elapsed
## 12.37 0.01 12.85 Note, I would expect using setDTthreads(1L) would minimize any impacts to performance but that does not appear to be the case on Windows 10.