• David Crawshaw's avatar
    runtime: remove defer from standard cgo call · 44150215
    David Crawshaw authored
    The endcgo function call is currently deferred in case a cgo
    callback into Go panics and unwinds through cgocall. Typical cgo
    calls do not have callbacks into Go, and even fewer panic, so we
    pay the cost of this defer for no typical benefit.
    
    Amazingly, there is another defer on the cgocallback path also used
    to cleanup in case the Go code called by cgo panics. This CL folds
    the first defer into the second, to reduce the cost of typical cgo
    calls.
    
    This reduces the overhead for a no-op cgo call significantly:
    
    	name       old time/op  new time/op  delta
    	CgoNoop-8  93.5ns ± 0%  51.1ns ± 1%  -45.34%  (p=0.016 n=4+5)
    
    The total effect between Go 1.7 and 1.8 is even greater, as CL 29656
    reduced the cost of defer recently. Hopefully a future Go release
    will drop the cost of defer to nothing, making this optimization
    unnecessary. But until then, this is nice.
    
    Change-Id: Id1a5648f687a87001d95bec6842e4054bd20ee4f
    Reviewed-on: https://go-review.googlesource.com/30080
    Run-TryBot: David Crawshaw <crawshaw@golang.org>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: 's avatarIan Lance Taylor <iant@golang.org>
    44150215
cgocall.go 19.6 KB