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Rick Hudson authored
Add to each span a 64 bit cache (allocCache) of the allocBits at freeindex. allocCache is shifted such that the lowest bit corresponds to the bit freeindex. allocBits uses a 0 to indicate an object is free, on the other hand allocCache uses a 1 to indicate an object is free. This facilitates ctz64 (count trailing zero) which counts the number of 0s trailing the least significant 1. This is also the index of the least significant 1. Each span maintains a freeindex indicating the boundary between allocated objects and unallocated objects. allocCache is shifted as freeindex is incremented such that the low bit in allocCache corresponds to the bit a freeindex in the allocBits array. Currently ctz64 is written in Go using a for loop so it is not very efficient. Use of the hardware instruction will follow. With this in mind comparisons of the garbage benchmark are as follows. 1.6 release 2.8 seconds dev:garbage branch 3.1 seconds. Profiling shows the go implementation of ctz64 takes up 1% of the total time. Change-Id: If084ed9c3b1eda9f3c6ab2e794625cb870b8167f Reviewed-on: https://go-review.googlesource.com/20200Reviewed-by:
Austin Clements <austin@google.com>
40934815
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