host.Init forked processes persist and maintain high CPU load

[BrockMatthews]

Describe the bug Processes spawned by host.Init() when using ftdi maintain a high CPU load on multiple threads that persists.

To Reproduce Steps to reproduce the behavior:

1. Run program

package main

import (
	"log"
	"runtime"
	"time"

	"periph.io/x/host/v3"
	"periph.io/x/host/v3/ftdi"
)

func main() {
	host.Init()
	log.Println("Init done.")

	ftdi.All()

	buffer := make([]byte, 1024)
	runtime.Stack(buffer, true)

	log.Println("Running goroutines:")
	log.Println(string(buffer))

	time.Sleep(1 * time.Hour)
}

2. Run it.

2023/10/04 00:05:43 Init done.
2023/10/04 00:05:43 Running goroutines:
2023/10/04 00:05:43 goroutine 1 [running]:
main.main()
	/home/name/go/src/periphio_test/test.go:19 +0x78

3. Check process

# top -H -p <test PID>

Threads:  12 total,   0 running,  12 sleeping,   0 stopped,   0 zombie
%Cpu(s):  4.7 us, 19.3 sy,  0.0 ni, 75.7 id,  0.0 wa,  0.0 hi,  0.3 si,  0.0 st
KiB Mem :  3074384 total,  2296660 free,   562180 used,   215544 buff/cache
KiB Swap:        0 total,        0 free,        0 used.  2406060 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND                                                                                                                                               
 5264 name      20   0 1327928  14104   3280 S 13.0  0.5   0:08.36 test_aa                                                                                                                                       
 5278 name      20   0 1327928  14104   3280 S 12.6  0.5   0:08.72 test_aa                                                                                                                                       
 5277 name      20   0 1327928  14104   3280 S 10.0  0.5   0:06.38 test_aa                                                                                                                                       
 5262 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.01 test_aa                                                                                                                                       
 5263 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.00 test_aa                                                                                                                                       
 5265 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.00 test_aa                                                                                                                                       
 5266 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.01 test_aa                                                                                                                                       
 5267 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.00 test_aa                                                                                                                                       
 5268 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.00 test_aa                                                                                                                                       
 5269 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.00 test_aa                                                                                                                                       
 5270 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.00 test_aa                                                                                                                                       
 5279 name      20   0 1327928  14104   3280 S  0.0  0.5   0:00.00 test_aa

Expected behavior No processes to persist and produce high CPU load after host.Init() completion.

Platform (please complete the following information):

• OS: NXP i.MX Release Distro 4.14-sumo (sumo)
• Board: custom

Additional context Device: FTDI FT232H

Device is completely usable after host.Init()

ftdi_sio driver unbound from used FT232H, but module not removed as it is required by other FTDI devices on the system.

[maruel]

This is surprising. Can you use https://pkg.go.dev/runtime/pprof to try to determine what is spinning? Keep in mind the ftdi driver is known to not be at the quality bar that the project generally aims to achieve.

[BrockMatthews]

Thanks. The profiling output isn't awfully specific but here it is

Duration: 10.21s, Total samples = 5.66s (55.44%)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top
Showing nodes accounting for 5660ms, 100% of 5660ms total
      flat  flat%   sum%        cum   cum%
    2390ms 42.23% 42.23%     2390ms 42.23%  [libpthread-2.27.so]
    2330ms 41.17% 83.39%     2330ms 41.17%  runtime._LostExternalCode
     840ms 14.84% 98.23%      840ms 14.84%  [libc-2.27.so]
     100ms  1.77%   100%      100ms  1.77%  [PeriphioTest_aarch64]
         0     0%   100%     5660ms   100%  runtime._ExternalCode

Please let me know of anything else I can provide.

[maruel]

Sorry I won't be able to diagnose with this data. You will likely need to investigate more deeply yourself.

[BrockMatthews]

On deeper inspection the issue seems to be caused by the ftd2xx driver with the call to FT_Open in d2xx_posix.go open(). This happens specifically on the device that is used and has ftdi_sio unbound, and on none of the other FTDI devices iterated through.