you need to keep a bunch of per-cpu ("per-core") kernel threads and you
need to make sure not to starve them, but for a short test that's okay. oh,
and don't have any processes running that use io uring...
On Friday, September 27, 2024 at 5:37:53 PM UTC+2 robert engels wrote:
> Also, you can configure the kernel at boot to exclude certain cpus from
> the OS completely so no process can interfere with them - BUT -
> processes/threads can still be moved to these isolated cpus using
> setsched().
>
> On Sep 27, 2024, at 10:34 AM, robert engels <ren...@ix.netcom.com> wrote:
>
> What you want to do is start the process with a cset to restrict the cores
> it can use - then use the setsched to move certain threads to cores that
> have been excluded.
>
> On Sep 27, 2024, at 10:26 AM, 'TheDiveO' via golang-nuts <
> golan...@googlegroups.com> wrote:
>
> Are you running this on a multi-core? Your non-fifo tasks can be scheduled
> to other cores, et cetera. BTW, fifo 99 is a recipe for desaster as it can
> starve the kernel on a core, preventing necessary kernel house-keeping.
> Don't ask me how I know...
>
> What is the reason for setting GOMAXPROCS, I'm at a loss here, so
> appreciating help! IIRC, OS-thread locked goroutines don't count against
> this limit.
>
> This looks like a situation where I personally would fire off recording
> kernel scheduler tracepoint events and then having a close look at in
> kernelshark at what really is going on. There are syscalls in the FIFO
> scheduled path that might cause preemption. I would look at sched_switch
> here, as well as sched_switch_new. Maybe print the TIDs so you can find
> your go-routine related tasks in all the scheduler event noise, but maybe
> the binary's comm (name) might be already sufficient if you give it a
> catchy name.
>
> A steeper learning curve would be to prepare a bpftrace script matching on
> the comm/name on the scheduler trace events, to get an idea of whats going
> on.
>
> On Thursday, September 26, 2024 at 5:49:53 AM UTC+2 Zhao Weng wrote:
>
>> Hi gophers,
>> I'm doing a research on how to prioritise some goroutines over others.So
>> I can allocate more CPU resource to more important part of the program.
>> I try to do it by calling runtime.LockOSThread to assign the goroutine
>> needs to be prioritise to a designated OS thread, and unix.SchedSetAttr to
>> prioritise that OS thread. Here is the code:
>>
>> ```go
>> package main
>>
>> import (
>> "flag"
>> "fmt"
>> "runtime"
>> "sync"
>> "time"
>>
>> "golang.org/x/sys/unix"
>> )
>>
>> var (
>> nPrioritizedGoroutines = flag.Int("p", 1, "# of prioritized goroutines")
>> nNormalGoroutines = flag.Int("n", 1, "# of normal goroutines")
>> restDuration = flag.Duration("r", 0, "rest for a certain amount of time
>> between works")
>> )
>>
>> func prioritizeThread() {
>> // set thread priority to the highest
>> a := unix.SchedAttr{
>> Size: unix.SizeofSchedAttr,
>> Policy: 1,
>> Priority: 99,
>> }
>>
>> if err := unix.SchedSetAttr(0, &a, 0); err != nil {
>> panic(err)
>> }
>> }
>>
>> func doWorks(workerId int) {
>> t := time.Now()
>> for i := 0; i < 100; i++ {
>> st := time.Now()
>> res := 0
>> for ii := 0; ii < 1e9; ii++ {
>> res += ii
>> }
>> fmt.Printf("%d@%d, timecost: %s, res: %d \n", workerId, unix.Gettid(),
>> time.Since(st), res)
>>
>> // sleep for a while to simulate gaps between requests.
>> if *restDuration > 0 {
>> time.Sleep(*restDuration)
>> }
>> }
>> fmt.Printf("total execute time for worker: %d is %s\n", workerId, time.
>> Since(t))
>> }
>>
>> func main() {
>> flag.Parse()
>>
>> runtime.GOMAXPROCS(*nPrioritizedGoroutines)
>> var wg sync.WaitGroup
>>
>> workerId := 0
>> for i := 0; i < *nPrioritizedGoroutines; i++ {
>> wg.Add(1)
>> go func(workerId int) {
>> // assign goroutine to a designated thread
>> runtime.LockOSThread()
>> // prioritize this thread
>> prioritizeThread()
>>
>> defer wg.Done()
>> doWorks(workerId)
>> }(workerId)
>> workerId++
>> }
>>
>> for i := 0; i < *nNormalGoroutines; i++ {
>> wg.Add(1)
>> go func(workerId int) {
>> defer wg.Done()
>> doWorks(workerId)
>> }(workerId)
>> workerId++
>> }
>>
>> wg.Wait()
>> }
>> ```
>> compile on linux, and run with command `sudo ./sche`, it seems not
>> working, CPU resource is shared by two thread, and two goroutine execute `
>> doWorks` in similar timecost(1.5 seconds).
>>
>> sudo ./sche
>> 1@255429, timecost: 1.475347182s, res: 499999999500000000
>> 0@255425, timecost: 1.517077413s, res: 499999999500000000
>> 1@255429, timecost: 1.473167148s, res: 499999999500000000
>> 0@255425, timecost: 1.515322146s, res: 499999999500000000
>> 1@255429, timecost: 1.494751901s, res: 499999999500000000
>> 0@255425, timecost: 1.532692691s, res: 499999999500000000
>>
>> while with 1 goroutine only, the timecost will be 0.75 seconds
>>
>> sudo ./sche -n 0
>> 0@257072, timecost: 751.18938ms, res: 499999999500000000
>> 0@257072, timecost: 747.364725ms, res: 499999999500000000
>> 0@257072, timecost: 745.362553ms, res: 499999999500000000
>> 0@257072, timecost: 748.353778ms, res: 499999999500000000
>>
>> Am I doing anything wrong here?
>>
>> Zhao Weng
>>
>
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