Assembly incurs a function call cost (non-inlineable AFAIU), but Cgo incurs a function call cost with additional work for C stack and call conventions translation as said by Tamás.
On Fri, 2019-03-01 at 08:13 -0800, Jason E. Aten wrote: > 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 > -- 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.
