On Thu, Aug 15, 2019, 05:19 sandao <yirenwe...@gmail.com> wrote:
> In my opinion, the slice which "as" point to, is all allocated on the
> heap in two case . so, I think the mark time should not be so different.
> Can you tell me more details for you answer(when as is allocated on the
> stack, gc has a smaller task.)?
>
> 在 2019年8月15日星期四 UTC+8上午11:02:46，Gergely Födémesi写道：
>>
>> .On Wed, Aug 14, 2019, 17:56 sandao <yiren...@gmail.com> wrote:
>>
>>> type A struct {
>>> a int
>>> }
>>>
>>> func gen() []*A {
>>> r := make([]*A, 1000000)
>>> for i := 0; i < len(r); i++ {
>>> r[i] = &A{i}
>>> }
>>> return r
>>> }
>>>
>>> //var as []*A = gen()
>>>
>>> func main() {
>>> go func() {
>>> err := http.ListenAndServe(":8034", nil)
>>> if err != nil {
>>> //fmt.Printf("ListenAndServe:%s\n", err)
>>> }
>>> }()
>>> var as []*A = gen()
>>> fmt.Println(as[0])
>>> time.Sleep(100 * time.Second)
>>> }
>>>
>>> when debug gc:
>>> 1) if the "var as []*A = gen()" is in main , the debug info is : gc
>>> 4 @2.757s 0%: 0.049+0.59+0.025 ms clock, 2.3+0/0.54/0.28+1.2 ms cpu,
>>> 16->16->0 MB, 31 MB goal, 48 P (forced)
>>> 2) if the "var as []*A = gen()" is not in main, the debug info
>>> is: gc 9 @7.172s 0%: 0.077+25+0.020 ms clock, 3.7+0/24/0.73+0.99 ms
>>> cpu, 16->16->15 MB, 31 MB goal, 48 P (forced)
>>>
>>> Anybody konw why the mark time (red numbers) is so different?
>>>
>>
>> when as is allocated on the stack, gc has a smaller task.
>>
>
see for yourself what the compiler says about that decision:
https://golang.org/cmd/compile/
you'll need -m
you can also use pprof to check your assumptions.
(there isn't any computer near me currently)
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