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Old 10-05-2014, 05:41 PM   #1
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Operating System thread switching and saving

I am not sure if this is the best sub for my question... I hope though that the mods can help me move the thread to appropriate place if I misplace it.
I am currently in a operating system class, and I have a question related to thread switching and save the previous thread when switch. So the question is like this:
The use of Hardware Threads or Hyper-threading is becoming commonplace in the design of 
new processors. For example, the Core i3 and i5 lines include hardware provisions to handle two 
hardware threads per processor (core). This is done by duplicating those parts of the processor 
that store the architectural state, namely, the control and general purpose registers, but not 
duplicating the main execution resources (e.g., pipelining). In short, only one of the hardware 
threads can be executing, but each one of the two hardware threads has its own set of registers.
Assume that your architecture has two cores (processors), each equipped with two hardware 
threads. Assume you are running a process composed by 8 threads, each connecting to a 
lightweight process (thus, visible to the kernel as kernel threads). Each of the threads repeats the 
following cycle a large number of times:
CPU usage 10ms, I/O 10ms
Assume that the scheduler switches threads every 5 ms. Fill out a table like the following, indicating the 
state of each of the threads at every interval. Also, indicate, by the symbols S, and NS whether the 
switch caused the saving (or not) of the architectural state of the preempted thread. Assume that no 
other process or thread is present in the system.
5ms 10ms 15ms 20ms 25ms 30ms 35ms 40ms 45ms 50ms 55ms 60ms
I know that because there is 2 Hardware threading in 1 processor, so the process could have 2 thread run concurrently... and when it switch from T1 and T2 to T3 and T4, T1 and T2 go to ready state. How do the saving of the thread happen? According to the solution my professor give, the saving of T1 and T2 only occur when T5 and T6 go to the running state, but not when T3 and T4 at the running state. My question is why it doenst save immediately when it switch to T3 and T4 threads?
Old 10-06-2014, 06:38 AM   #2
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Why not ask him/her?
Old 10-06-2014, 08:10 AM   #3
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Originally Posted by JeremyBoden View Post
Why not ask him/her?
Because it was weekend. It would be great if I get some answer from here though. Isnt this forum LinuxQuestions??? ._.


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