2019. március 1., péntek 17:13:28 UTC+1 időpontban Jason E. Aten a következőt írta: > > If I include a chunk of assembly .s code in my Go code, does my program > pay the CGO transition cost of locking and changing to a C stack? > > I'm pretty sure the answer is no. But my knowledge of the Go internals is > low enough that I thought I would like confirm that before I go pulling in > .s code. > > Then for numerical work, if I need to call some Fortran 90 compiled > library routines, does it not just look like assembly? I suppose not... in > the sense that it makes certain assumptions about being able to grow the > stack it is running on without running out of space. Are there assumptions > beyond the stack that are used? Probably some "standard library" runtime > dependencies? > > So on to my central question: Can the CGO transition stack switching cost > be minimized by telling Go to run my main (single threaded) Go routine on a > C thread to start with? In other words, can I minimize the CGO switching > cost by doing runtime.LockOSThread() or similar? > > It seems like if we are already on a C thread, then perhaps *some large > part* of the cost of Go -> f90 can be avoided. Of course the Go compiler > doesn't know we are on a C thread in the general case, right(?), so it > probably can't optimize those transitions by omitting change-the-stack code. > > Returning to the original throught about .s code, what would happen if > that code tried to grow the stack too far? Just crash? Is there guidance > about how far assembly can grow the stack before it needs to check back > with the runtime? > > Thanks! > > J >
AFAIK asm parts are compiled into the binary, and no overhead is paid. For cgo, it is not just stack growth, but the differences between C and Go calling convention, the "ABI". So LockOSThread may help, but won't eliminate all the overhead. Do you really have to pay that overhead a lot of times? Can't you batch the calls? Tamás Gulácsi -- 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. For more options, visit https://groups.google.com/d/optout.
