[Rd] Detecting physical CPUs in detectCores() on Linux platforms

[Dirk Eddelbuettel]

On 8 August 2023 at 11:21, Simon Urbanek wrote:
| First, detecting HT vs cores is not necessarily possible in general, Linux may assign core id to each HT depending on circumstances:
| 
| $ grep 'cpu cores' /proc/cpuinfo | uniq
| cpu cores	: 32
| $ grep 'model name' /proc/cpuinfo | uniq
| model name	: Intel(R) Xeon(R) Gold 6142 CPU @ 2.60GHz
| 
| and you can look up that Xenon 6142 has 16 cores.
| 
| Second, instead of "awk"ward contortions it's easily done in R with something like
| 
| d=read.dcf("/proc/cpuinfo")
| sum(as.integer(tapply(
|   d[,grep("cpu cores",colnames(d))],
|   d[,grep("physical id",colnames(d))], `[`, 1)))
| 
| which avoids subprocesses, quoting hell and all such issues...

Love the use of read.dcf("/proc/cpuinfo") !!

On my box a simpler

  > d <- read.dcf("/proc/cpuinfo") 
  > as.integer(unique(d[, grep("cpu cores",colnames(d))]))
  [1] 6
  > 

does the right thing.

Dirk

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