Yes you are right, P is a logical processor holding LRQ of go-routines On Thursday, May 14, 2020 at 1:44:57 PM UTC-7, Ian Lance Taylor wrote: > > On Thu, May 14, 2020 at 9:28 AM <overex...@gmail.com <javascript:>> wrote: > >> I learnt that, >> >> the reason we have context(`P`) introduced in Goruntime, is that we can >> hand them off(it's LRQ of goroutines) to other OS thread(say `M0`), if the >> running OS thread(`M1`) needs to block for some reason. >> >> >> [image: Untitled.png] >> >> >> ------------------------------ >> >> Above, we see a thread(`M1`) giving up its context so that another >> thread(`M0`) can run it. The Go scheduler makes sure there are enough >> threads to run all contexts(`P1`, `P2`, `P3` etc..). >> >> >> ---------------- >> >> Above model is `M:N` [threading model]( >> https://cs.stackexchange.com/questions/1074/what-is-the-purpose-of-mn-hybrid-threading), >> >> where each OS thread(`M1`) running on CPU core(`C`) assigned a context(`P`) >> having `K` goroutines in it's LRQ. >> >> vis-a-vis >> >> `1:1` threading model, where each core(`C`) has one OS thread(`M`). >> `pthread_create()`. >> >> Comparing above two threading models, context switching of go-routines(in >> `M:N` threading model) is much faster than context-switching of OS >> threads(in `1:1` threading model) >> >> -------------------------- >> >> To understand the purpose of context(`P`), >> >> what is the advantage of handing off context(`P1`) to other thread(say >> `M2`) running on core(`C2`)? >> >> Is the advantage about efficiency in re-using cache lines(L1/L2) on core >> `C2`, for the related set of goroutines sitting in LRQ of context(`P1`)? >> > > > What do you mean when you write context(`P`)? By that do you simply mean > what the runtime package calls a P? A P is a logical processor; see the > long comment at the top of runtime/proc.go. > > Ian >
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