https://software.intel.com/en-us/ar...ding-technology

Open book 也看不太懂

pipelining:
it is a technique for a cpu to perform every single instruction with a fixed clock-cycle and fixed execution-stages.

superscalar:
with a capability of pipelining, a cpu is able to execute, at least, two or more instructions at the same time.

hyper-threading:
it is a kind of technique of duplicating a register file inside of cpu in order to make the cpu be able to execute two programs at the same time if the execution unit is available. [it does not matter how many instruction cpu has to perform.]

it pretends that there are two cpus inside of a chip. because there are two register file inside of cpu.
it can perform two program at the same time if there is an execution unit which is available.
this method is almost the same as multi-core. however, it can not replace a real multi-cored cpu if all the execution units are unavailable.
once the circumstance happened, the performance of program will degrade. further, it will waste more time on switching program. usually it will stall and held rest of other programs that perform in background and it only performs one program which is in foreground. yes, it is. only single one program.

remember: all the program may probably have their own sub-procedures or functions.
that is the key we do not treat hyper-threading is equal to threading.

multi-core:
it is a technique to bundle multiple cpus inside a chip in order to be able to execute multiple program at the same time.

for example: there are two games. one is GTA5. another is age of empire 3.
both games are allocated separately in different core. it will greatly improve the performance of both games.
it is because of every game executes in different core with no interference.

threading:
a tricky technique derived from time-sharing operating system.
it allows a program divided into multiple sub-procedures or functions. each sub-procedures or functions can be duplicated infinitely.

let us assume a DVD player software is a program. and it includes a function called video screen.
you can play two DVD movies within the DVD player software but creating two windowed screens by calling function video screen for each DVD movie.

for example: there is a DVD player software that is playing a movie. however, you want to see two movies at the same time. all you need to do is just to open another DVD iso file inside of the DVD player software. and let the DVD player software have two windowed screens of the movie you played.
then, you can see the movies in one DVD player software with two windowed screens inside at the same time.

most of time, we can treat hyper-threading and threading are the same in some aspects.
it depends on how the architecture of operating system will be designed and organized.

OS裡的thread , 之所以是稱之為線程 , 就是因為它不同於sub-procedure !!

就我所瞭解的OS裡的thread , 本身不含任何的程式碼 ,它只是很單純的data structure
更簡單說,它只是資料而已,所以才稱為thread , 如果它本身含有程式碼+資料 , 那就直接稱為
process/procedure就好,沒事去多弄一個名稱thread , 來搞得我好亂做什麼呢??

如果,你不去套用任何的現成Library 單純從無到有來設計thread化的program , 那真的如同設計一個OS 一樣的不容易 , 同樣的如果你能夠設計出來,就真的代表你徹底搞清楚何謂thread !!

因為HT的漏洞越補越多，乾脆直接拿掉比較快…

the reason we divided a program into multiple sub-procedure is to execute multiple duplicated copy of data.

like i said above, you want to see two movies at the same time.
you can have two DVD player programs that perform each DVD movie at the same time.

but it would be inefficient. the best way for you to do the same is to make the DVD player program become a sub-procedure or a function.
you can have unlimited DVD data you want in a program which is performed by the sub-procedure or function.

imaging. you got one video player software which is playing a DVD movie and a BD movie at the same time.
do you think that the DVD decoder is able to decode BD data?
you might say why i need to use DVD decoder to decode BD data? why do i not use BD decoder to decode DVD data.

the key point is you will never know what your thread will need to do.
you can think that there are two threads only performing the function of windowed screen separately for DVD and BD.
however, there is also a thread performing the task of issuing subtitles onto each windowed screen.

do you think that the function (or you can call the function a thread) of issuing subtitles and performing windowed screen would be the same?

the answer is NO.
although they are in the same video player software.

老實說,我不喜歡這個例子的說明!! 那只會把觀念搞得更亂....

實務上的例子,我想不出來除了Apache 這個web server以外更好的例子 !!
但....

我想沒有人有興趣去鑽研它,只為了徹底瞭解thread !!

figure 1: the example of user level thread.


figure 2:the example of system level thread.

different technique of threading between OS aspect and Software aspect

你就這樣想 CPU 如何挑選


博士生有兩隻手


高中生也是



1.你端盤子要用一隻手或兩隻手，效率肯定不一樣，兩隻手就好比開了 HT


2.當你算數學題目，你的手有幾隻，那對運算答案沒有太大幫助，就好比實體核心數，靠的是大腦。


3.再來就是你到底是要請博士生來端盤子，還是高中生來端盤子，


如果是端盤子，越多人越好，而且高中生就可以了


但是你解數學題目，你請再多的高中生也沒用阿


再來另一個環節，目前的多核心運算就跟騎協力車一樣，


並不是人越多，車子就騎越快，當然這台車子的架構設計到底可以幾個人騎達到最高效能

就跟軟硬體能否與多核心與時俱進的成長是有關的..

的確簡單明瞭。

本人非相關科系。想再請教CUP在做哪些事屬於端盤子，做哪些事屬於做計算？