|
||
|
Advance Member
  
加入日期: Mar 2004 您的住址: 星寶樂園
文章: 384
|
Prescott架構的問題(爬文ed)
假設我們有個k-stage的pipeline,每clock cycle time為T.
現在我們有n條指令(or task) 則時間應為k*T+(n-1)*T=(k+n-1)*T 而沒pipeline時間為n*k*T 因此速度增加的比率為n*k*T/(k+n-1)*T 對n取極限(->無限大),得出k,即理論上k條pipeline會比無pipeline快上k倍 ------------------------------------------------------------ 為什麼我要提這? 因為之前看某大大說prescott是因為stage多總和時間變長 效能才低落 有點和上面起衝突  |
|||||||
2004-04-27, 06:53 PM
#1
|
|
|
Power Member
 加入日期: Mar 2003 您的住址: 台北
文章: 597
|
回覆: Prescott架構的問題(爬文ed)
引用:
你說的是在完全理想的狀況下的確是這樣沒錯(計算機概論有教) 但是真實的程式也許許多多的分支 譬如說當要等上ㄧ行的值出來才能算這一行的值時 它的31階管線就變成致命傷了(在等待值的時候管線全空不能跑) 而在程式中分支出現的機率相當大 當初有人算過約在8階管線可以達到最好的IPC 超過或減少都會損失IPC 目前P4的管線過程以至於在面對複雜的運算的時候效能爛八八也是這樣 即使不斷用時脈彌補 但是很多地方仍不及時脈低ㄧ大截的其他cpu 你應該是剛開始學或看計算機架構吧 那些說到的都是最基本的理論部份 真實cpu效能分析沒那麼簡單 所以才會造成您的疑惑 |
|||
|
2004-04-27, 07:13 PM
#2
|
|
|
Master Member
加入日期: Feb 2004 您的住址: 加拿大
文章: 2,391
|
回覆: Prescott架構的問題(爬文ed)
引用:
沒錯,這是理論上,管線越長時脈越快,處理速度也應該越快,但是還是牽涉到其他的問題 舉例來說,若是再"K-1"stage的地方出問題,就要重新來過,這要把之前已經在pipline裡的東西倒掉,空出整個單元給這個出錯的計算. 這個過程會嚴重的拖慢CPU的速度,所以管線越長,Branch prediction table就要越好越精確,以減少預測錯誤造成的延遲. 另外,管線越長,級數越多,最好就要保持管線時時都在"工作",才能展現長管線的高速處理優勢. 從Prescott的表現來看,Intel加強了分支預測來減少錯誤造成的延遲,並增加了L2快取來保持管線的"忙碌"
__________________
Rule #12: Never date a co-worker. Rule #13: Never involve lawyers. Rule #23: Never mess with a Marine's coffee if you want to live! Rule #51: Sometimes you are wrong 純白の吸血鬼は微笑む：私を殺した責任、とってもらうからわ - アルクエイド ブリュンスッド 貴方に出逢い STAR輝いて アタシが生まれて Was aus Liebe gethan wird, geschieht immer Jenseits von Gut und Böse - Friedrick Wilhelm Nietzsche Cain was the first man ever to strike down another... and when the Lord came to him and said ‘What have you done!?’, Cain could not hide his crime. For the voice of his brother’s blood cried out from the very ground The world has been your battlefield, everywhere you go. The blood of brothers and sons screams out against you. Perhaps you cannot yet hear it, because the soil is not your own, but you will... you will |
|
|
2004-04-27, 07:15 PM
#3
|
|
|
Advance Member
加入日期: Mar 2004 您的住址: 星寶樂園
文章: 384
|
恩恩,是data dependencies和conditional branch statemnets
我也有讀到,不知是不是因為這樣 我真的是聽到那句話有疑問的 怕說先打了會被認為是自問自答= =a 不過還真的是跟計概課本一樣阿  這就是傳說中的"應用課本知識"嗎XD ------------------------------------------------------- 對了,好像prescott的效能問題也有hit rate這種東西? 看太多文章搞混了  |
|
2004-04-27, 07:37 PM
#4
|
|
|
Master Member
加入日期: May 2001
文章: 2,239
|
提外話，管它現在管線深不深，反正三年後INTEL會將DT與MOBILE整合(終於不再追時脈了)，CPU核心都是共用，相信耗電量將會下降很多，之後就不用太擔心THERMAL的問題了，核心代碼聽說是Merom還有啥Jonah...在那之前，出的東西都是為了黑錢...ㄎㄎ 這樣浪費資源的東西也拿出來賣...
|
|
2004-04-27, 07:38 PM
#5
|
|
|
Elite Member
加入日期: Aug 2001
文章: 12,393
|
引用:
呵呵..又改了...之前很像聽說會和XEON合而為一...  |
|
|
2004-04-27, 07:40 PM
#6
|
|
|
Master Member
加入日期: Feb 2004 您的住址: 加拿大
文章: 2,391
|
引用:
是merom, Yonah是為Merom鋪路,率先整合多核心,一顆Yonah等於兩顆Dothan,估計會再2005下半推出,同時桌上型會使用Tejas(約2005Q2~), Cedarmill(主流,進階), Tulsa(XE) (約2005下半~2006中), 2006年約Q2~Q3會全面整合為Merom
__________________
Rule #12: Never date a co-worker. Rule #13: Never involve lawyers. Rule #23: Never mess with a Marine's coffee if you want to live! Rule #51: Sometimes you are wrong 純白の吸血鬼は微笑む：私を殺した責任、とってもらうからわ - アルクエイド ブリュンスッド 貴方に出逢い STAR輝いて アタシが生まれて Was aus Liebe gethan wird, geschieht immer Jenseits von Gut und Böse - Friedrick Wilhelm Nietzsche Cain was the first man ever to strike down another... and when the Lord came to him and said ‘What have you done!?’, Cain could not hide his crime. For the voice of his brother’s blood cried out from the very ground The world has been your battlefield, everywhere you go. The blood of brothers and sons screams out against you. Perhaps you cannot yet hear it, because the soil is not your own, but you will... you will |
|
|
2004-04-27, 08:34 PM
#7
|
|
|
Master Member
加入日期: Feb 2004 您的住址: 加拿大
文章: 2,391
|
引用:
不會啦,兩個要求的完全不一樣...一個要求速度,另一個求穩定,再怎樣也不可能會將DT跟XEON合而為一,目前兩者的核心是共通的,只是在DT的CPU上面屏蔽掉一些用不到的功能,或是加上一些如L3快取 接下來就要看intel是否打算連XEON都整合進DT/NB這條生產線
__________________
Rule #12: Never date a co-worker. Rule #13: Never involve lawyers. Rule #23: Never mess with a Marine's coffee if you want to live! Rule #51: Sometimes you are wrong 純白の吸血鬼は微笑む：私を殺した責任、とってもらうからわ - アルクエイド ブリュンスッド 貴方に出逢い STAR輝いて アタシが生まれて Was aus Liebe gethan wird, geschieht immer Jenseits von Gut und Böse - Friedrick Wilhelm Nietzsche Cain was the first man ever to strike down another... and when the Lord came to him and said ‘What have you done!?’, Cain could not hide his crime. For the voice of his brother’s blood cried out from the very ground The world has been your battlefield, everywhere you go. The blood of brothers and sons screams out against you. Perhaps you cannot yet hear it, because the soil is not your own, but you will... you will |
|
|
2004-04-27, 08:44 PM
#8
|
|
|
Master Member
加入日期: Feb 2004 您的住址: 加拿大
文章: 2,391
|
引用:
較大的快取雖然有助於填滿管線以增進效能,但是另一方面會拉大搜尋時間,而降低效能 搜尋時間可用高時脈來縮短,所以Prescott的真正實力可能真的如Intel說的,要在高時脈下才能顯現
__________________
Rule #12: Never date a co-worker. Rule #13: Never involve lawyers. Rule #23: Never mess with a Marine's coffee if you want to live! Rule #51: Sometimes you are wrong 純白の吸血鬼は微笑む：私を殺した責任、とってもらうからわ - アルクエイド ブリュンスッド 貴方に出逢い STAR輝いて アタシが生まれて Was aus Liebe gethan wird, geschieht immer Jenseits von Gut und Böse - Friedrick Wilhelm Nietzsche Cain was the first man ever to strike down another... and when the Lord came to him and said ‘What have you done!?’, Cain could not hide his crime. For the voice of his brother’s blood cried out from the very ground The world has been your battlefield, everywhere you go. The blood of brothers and sons screams out against you. Perhaps you cannot yet hear it, because the soil is not your own, but you will... you will |
|
|
2004-04-27, 10:32 PM
#9
|
|
|
Elite Member
加入日期: Apr 2004 您的住址: 港都
文章: 6,019
|
基本上有用到caching運作，如level 1 / 2 / 3 cache，儲存裝置的buffer等，都會牽扯到hit rate(命中率)。其實快取機制運行時，會需要一些演算及指令預測，讓控制器去猜測到下一輪存取可能會用到的資料，將其抓進來，所以若是命中率高，就不用去對主計憶體進行存取，所以快取系統不僅要大，也要講究高命中率。
|
|
2004-04-27, 10:55 PM
#10
|
|
