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https://github.com/golang/go
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e9079a69f3
This implements runtime support for buffered write barriers on amd64. The buffered write barrier has a fast path that simply enqueues pointers in a per-P buffer. Unlike the current write barrier, this fast path is *not* a normal Go call and does not require the compiler to spill general-purpose registers or put arguments on the stack. When the buffer fills up, the write barrier takes the slow path, which spills all general purpose registers and flushes the buffer. We don't allow safe-points or stack splits while this frame is active, so it doesn't matter that we have no type information for the spilled registers in this frame. One minor complication is cgocheck=2 mode, which uses the write barrier to detect Go pointers being written to non-Go memory. We obviously can't buffer this, so instead we set the buffer to its minimum size, forcing the write barrier into the slow path on every call. For this specific case, we pass additional information as arguments to the flush function. This also requires enabling the cgo write barrier slightly later during runtime initialization, after Ps (and the per-P write barrier buffers) have been initialized. The code in this CL is not yet active. The next CL will modify the compiler to generate calls to the new write barrier. This reduces the average cost of the write barrier by roughly a factor of 4, which will pay for the cost of having it enabled more of the time after we make the GC pacer less aggressive. (Benchmarks will be in the next CL.) Updates #14951. Updates #22460. Change-Id: I396b5b0e2c5e5c4acfd761a3235fd15abadc6cb1 Reviewed-on: https://go-review.googlesource.com/73711 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Rick Hudson <rlh@golang.org> |
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