> Your sample code above is entering the scheduler
continuously, which is not a typical characteristic of a real program
that has heavy CPU usage. It's possible that what you are seeing is
contention on the scheduler lock.
Ian,
Don't understand your point. The sample code above actually has better
latency in my test even though it is is entering the scheduler
continuously according to you:
func (c *Connection) imitateEncodeAndSend() {
onFinish := time.Now().Add(8 * time.Microsecond)
for time.Now().Before(onFinish) {
runtime.Gosched()
}
}
And this code has 10 times worse latency in my test:
func (c *Connection) imitateEncodeAndSend() {
onFinish := time.Now().Add(8 * time.Microsecond)
for time.Now().Before(onFinish) {
// runtime.Gosched()
}
}
On Monday, October 31, 2022 at 10:53:44 PM UTC+2 Ian Lance Taylor wrote:
> On Mon, Oct 31, 2022 at 1:34 PM Sergey Kurenkov
> <sergey.a...@gmail.com> wrote:
> >
> > I am trying to understand why higher CPU utilization leads to longer
> latency in reading from channels in golang. Could you help me with this
> question?
> >
> > I wrote a test that reads from channels and measure latency between
> writing to a channel and reading from the channel. It shows that the
> latency depends on CPU utulization. When one of functions looks like this
> >
> > func (c *Connection) imitateEncodeAndSend() {
> > onFinish := time.Now().Add(8 * time.Microsecond)
> > for time.Now().Before(onFinish) {
> > runtime.Gosched()
> > }
> > }
>
> You should make sure that you are testing CPU utilization itself,
> rather than heavy scheduler use. Sending a value on a channel
> generally requires a trip through the scheduler, to pick up the
> receiving goroutine and start running it. Often the scheduler can
> find the next job without acquiring the global scheduler lock, but not
> always. Your sample code above is entering the scheduler
> continuously, which is not a typical characteristic of a real program
> that has heavy CPU usage. It's possible that what you are seeing is
> contention on the scheduler lock.
>
> Ian
>
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