%CPU in 'procps' output for multi-cpu & hyperthreading (Thx for help)

Tom Rodman cygzw@trodman.com
Wed Oct 31 00:55:00 GMT 2007


[ a belated thank-you ] 

On Thu 10/11/07 19:52 BST Dave Korn wrote:
> On 11 October 2007 19:00, Matthew Woehlke wrote:
> 
> > Tom Rodman wrote:
> 
> >> I meant to ask:
> >> 
> >>   Is there a way to prove that a given process with more than 1
> >>   thread, must always have all it's threads on a single CPU at
> >>   any given time 
> 
>   Nope, because it's not the case.  In the absence of restricted affinity, the
> OS is free to schedule any ready thread to any free cpu at any time (although
> it will try to give a thread a quantum on the same cpu it ran on last time if
> possible, since that cpu might still have some of the thread's code or data in
> its L1 caches).  There is nothing special about threads happening to be from
> the same process or not and no guarantee that they will be on the same cpu -
> in fact, it goes to some trouble to distribute the threads within a process
> across all cpus.

Thanks sir!

>   There's some general discussion of the scheduler at
> http://book.itzero.com/read/microsoft/0507/microsoft.press.microsoft.windows.i
> nternals.fourth.edition.dec.2004.internal.fixed.ebook-ddu_html/0735619174/ch06
> lev1sec5.html
> (aka http://tinyurl.com/yonxs5 )

I have the 2005 'Windows Internals' hardcover - I'll read that section;
I appreciate the link.

>   See also the comment by "Mike Dimmick" at
> http://www.codinghorror.com/blog/archives/000671.html

been reading that discussion off and on, because of your link :->

>     cheers,
>       DaveK



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