Re:Linux: IO without entering the kernel
by amluto on Sunday December 16, 2018 @07:45PM
(#18696184)
Transitions from C0 to C1 and back are very fast [0], and basically any application has at least a core and probably several doing kernel things like servicing network IRQs.
I agree that HFT applications should not be using deep C states.
[0] Unless you have a misguided feature like C1E auto-promotion on. Fortunately, recent Linux kernels will overriding firmware and turn it off. On Sandy Bridge and possibly newer CPUs with C1E auto-promotion on, resuming from C1 can take many, many milliseconds.
I agree that HFT applications should not be using deep C states.
[0] Unless you have a misguided feature like C1E auto-promotion on. Fortunately, recent Linux kernels will overriding firmware and turn it off. On Sandy Bridge and possibly newer CPUs with C1E auto-promotion on, resuming from C1 can take many, many milliseconds.