![]() On sysmon to notice expired timers in some situations and sysmon can ParallelTimerLatency benchmark seen below. The benchmarks added in this CL measure that improvement in the To idle concurrently with timer creation using the same pattern usedįor submission of new goroutines in the same window.ĬL 232199, which was included in Go 1.15 improved timer latency over Goġ.14 by allowing P's to steal timers from P's not marked for preemption. This change also eliminates a race between a spinning P transitioning The required time, potentially stealing the new timer when it wakes. Wakes will determine how long to sleep and block on the netpoller for Have a scheduling opportunity before the new timer expires. Instead it wakes an idle P, if needed, whenĬreating a new timer because it cannot predict if the current P will Non-preemptable P's or relies on sysmon as a backstop to start threads With this change the scheduler no longer ignores timers on Other work would stop despite there being available work, missing the In addition, a spinning P that ignored an expired timer and found no That could take as long as 20ms if sysmon was in a 10ms Timers starved until the G running on their P completed or was That had the downside that any G's waiting on those expired ![]() ![]() Previously the scheduler ignored timers on P's not marked for The timers lock while running a timer function.Ĭhange-Id: I17792f5a0120e01ea07cf1b2de8434d5c10704ddĬhange the scheduler to treat expired timers with the same approach it Looking at the code, I don't see any reason why we have to hold I think this can happen if we change the deadlineįor a network connection exactly as the former deadline expires. Poll descriptor and the timers lock for some P may both be acquired inĭifferent order. So again there is a potential deadlock, in that the pd lock for some The timer function for poll descriptors winds up in netpolldeadlineimpl The pollSetDeadline function acquires pd.lock for some poll descriptor,Īnd in some cases calls resettimer which can in some cases acquire Issue 35532 describes another possible deadlock. It's not clear to me whether this deadlock can ever actually occur. The timers lock for some P may both be acquired in different order. So there is a potential deadlock, in that the scavenger lock and Which acquires the timers lock for the current P. Then calls resetTimer which can call addInitializedTimer The scavengeSleep function acquires the scavenger lock, The scavenger queues up a timer function that calls wakeScavenger, The timer code runs timer functions while holding the timers lock for a P. In fact, it is doubtful a sleep request for less than 10 us should even sleep at all - just call runtime.Gosched() since the overhead of a context switch is probably longer than the sleep request.ĭan Scales pointed out a theoretical deadlock in the runtime. I would expect the resulting runtime to be superior to Java and on par with C. There are probably very few threads using timers of this duration, so the overhead of allocating and blocking the thread shouldn't be that great. The simplest solution, although it doesn't work for channel select timeout, would be to have short duration time.Sleep() just invoke usleep(). I believe the performance issue in Go is due to multiple threads being involved (the timerproc, and the user routine) causing a lot of overhead. The following shows CPU utilization (on OSX). Interestingly, Java and Go use the same 'timeout on semaphore' to implement. ![]() The Go uses time.Sleep(), C uses usleep(), and Java uses LockSupport.ParkNanos(). I did some testing on this, comparing Go, C, and Java. The following Go program uses 20-25% %CPU as reported by top on Linux. However, I realised that both time.Ticker and time.Sleep() are causing excessive CPU overhead, probably due to runtime scheduling. I need to call a function roughly every millisecond, there is no real time requirement, as long as it is called roughly every millisecond everything is fine. GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build440058908=/tmp/go-build -gno-record-gcc-switches" What did you do? GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64" Yes What operating system and processor architecture are you using ( go env)? ![]() Go1.11 linux/amd64 Does this issue reproduce with the latest release? What version of Go are you using ( go version)? ![]()
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