On Sun, Mar 14, 2021 at 1:46 PM Robert Engels <reng...@ix.netcom.com> wrote: > > That was my point, based on Java, there is the ability to make the GC > coordination extremely efficient a read and two writes per Go to C complete > call trip - and this can often be eliminated in tight loops.
I don't mean to drag out the conversation but I'm not sure I understand the point. I think you were the first person to mention GC coordination. I don't think there is any GC coordination issue here. There is a scheduler coordination issue, specifically the need to inform Go's goroutine scheduler that the goroutine is changing behavior. Ian > So if the scheduling is the source of inefficiency there are more simple ways > to tackle than this proposal. > > > On Mar 14, 2021, at 3:04 PM, Ian Lance Taylor <i...@golang.org> wrote: > > > > On Sun, Mar 14, 2021 at 12:00 PM Robert Engels <reng...@ix.netcom.com> > > wrote: > >> > >> Based on two decades of Java FFI - the overhead comes from type mapping > >> not the housekeeping to control GC. The latter can be as simple as a > >> volatile read and 2 writes per call and can usually be coalesced in tight > >> loops. Since Go already has easy native C type mapping the FFi should be > >> very efficient depending on types used. > > > > Go and Java are pretty different here. The type mapping overhead from > > Go to C is effectively non-existent--or, to put it another way, it's > > pushed entirely onto the programmer The GC housekeeping is, as you > > say, low. The heaviest cost is the scheduling housekeeping: notifying > > the scheduler that the goroutine is entering a new scheduling regime, > > so that a blocking call in C does not block the entire program. A > > minor cost is the change is the calling convention. > > > > As Jason says, if all of the C code--and I really do mean all--can be > > compiled by a Go-aware C compiler, then the scheduling overhead can be > > largely eliminated, and pushed into the system call interface much as > > is done for Go code. But that is a heavy lift. Compiling only some > > of the C code with a Go-aware C compiler seems unlikely to provide any > > significant benefit. > > > > Ian > > > > > > > >> On Mar 14, 2021, at 11:37 AM, Jason E. Aten <j.e.a...@gmail.com> wrote: > >> > >> > I'm no authority here, but I believe a large (major?) part of the Cgo > >> overhead is caused by scheduling overhead. As I understand it, a C > >> function call is non-preemptible and the Go runtime don't know whether the > >> call will block. > >> > >> But that part would be handled by the C-compiler-that-knows-Go inserting > >> the pre-emption points just like the Go compiler does into the generated > >> code. Or the same checks for blocking. > >> > >> -- > >> You received this message because you are subscribed to the Google Groups > >> "golang-nuts" group. > >> To unsubscribe from this group and stop receiving emails from it, send an > >> email to golang-nuts+unsubscr...@googlegroups.com. > >> To view this discussion on the web visit > >> https://groups.google.com/d/msgid/golang-nuts/0ac6ac9e-ed99-4536-a8b0-44674f8b85a5n%40googlegroups.com. > >> > >> -- > >> You received this message because you are subscribed to the Google Groups > >> "golang-nuts" group. > >> To unsubscribe from this group and stop receiving emails from it, send an > >> email to golang-nuts+unsubscr...@googlegroups.com. > >> To view this discussion on the web visit > >> https://groups.google.com/d/msgid/golang-nuts/47869391-FC69-44C8-A7AA-8F335A17CF71%40ix.netcom.com. > > > > -- > > You received this message because you are subscribed to the Google Groups > > "golang-nuts" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to golang-nuts+unsubscr...@googlegroups.com. > > To view this discussion on the web visit > > https://groups.google.com/d/msgid/golang-nuts/CAOyqgcVSphZ4w%2BNaCFnkHOmoZ%2BOdD-Ob3K%2BbcjVn02fivJRX%2Bg%40mail.gmail.com. > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcXNJRiAPjejVzroX908XMtgOJqYyb0Nm0%2B5G8GFDfwk%2Bg%40mail.gmail.com.
