what is the rule of io-thread

[httaotao]

hi , I saw the video dev-session 8 , there were some questions about io-threads

1. how does the io-thread priority works ? I don't know why we should consider the fop priority and Can we change the fop priority ? I found that the code set the pri in conf , but when we create the thread, Will tasks be created first based on priority ?

2. I don't know the iot_worker, what is this and how does it work ? In code function , it has a conf param idle_time, it is contained in param enable-least-priority, I don't know how to use this param .

thanks

[pranithk]

hi , I saw the video dev-session 8 , there were some questions about io-threads

1. how does the io-thread priority works ?

This is explained in the video. Do let me know if something specific you didn't understand, I will try to explain it better.

I don't know why we should consider the fop priority and Can we change the fop priority ?

Priorities are brought in to give responsive user experience. So FOPs like LOOKUP/STAT etc get HIGH priority.

I found that the code set the pri in conf , but when we create the thread,

At the moment fop priorities are defined in the source file. So if you want to change them, you will have to modify source and re-compile and build new packages for yourself.

Will tasks be created first based on priority ?

Once the FOP comes to io-threads, they will get priority. Until then they won't have any priority.

2. I don't know the iot_worker, what is this and how does it work ? In code function , it has a conf param idle_time,

iot_worker is the function each io-thread executes. This is a thread-pool implementation. Roughly this is the work:

1. Each thread deques a fop from the lists of fops from the first client's priority queues.
2. After dequeuing a fop the next client comes to the head of the list of clients so that the next thread will pick fop from this clients queue.
3. It executes the fop and goes to step-1
4. If at any time there are no fops in the queues, then the thread waits for idle_time(configured as 120 seconds at the moment), if no operations comes during this time, the thread will terminate as long as the minimum number of threads are still running.
5. least-priority is used for internal clients like self-heal-daemon and rebalance. Only when there is no I/O from the users the I/O from these internal clients is picked up.

it is contained in param enable-least-priority, I don't know how to use this param .

If you want self-heal, rebalance to work similar to any other clients, you can disable it. At the moment user/application I/O is given more priority than the internal client I/O.

thanks

[httaotao]

thanks for answer. In video , you mentioned the function __iot_enqueue in io-threads.c. In this function ,I don't know how to set priorities here.
1.Is there a thread queue? If the operation is the high priority, it will be placed in the front of the queue, otherwise it will be placed in the back.
2.Or there is a second case, where there are multiple different queues, and high priority operations are placed in high priority queues.

Through these functions __iot_enqueue , list_add_tail and __iot_workers_scale, I can't be sure which one is. Maybe I don't know where the code is.

Combined with what you said before, can you provide architecture diagram or flow chart here.

thanks.

[pranithk]

thanks for answer. In video , you mentioned the function __iot_enqueue in io-threads.c. In this function ,I don't know how to set priorities here.
1.Is there a thread queue? If the operation is the high priority, it will be placed in the front of the queue, otherwise it will be placed in the back.
2.Or there is a second case, where there are multiple different queues, and high priority operations are placed in high priority queues.

There are multiple different queues. You can check iot_get_ctx() function call in __iot_enqueue() to understand this part.

Through these functions __iot_enqueue , list_add_tail and __iot_workers_scale, I can't be sure which one is. Maybe I don't know where the code is.

Combined with what you said before, can you provide architecture diagram or flow chart here.

This one will take time. Not sure when I will be able to spend time on this. I will update this thread, when I get time.

thanks.

[httaotao]

I get it , thanks