Re: [tlug] Re: /proc/uptime

["Stephen J. Turnbull" <stephen@example.com>]

Nguyen Vu Hung writes:
 > On Fri, Nov 14, 2008 at 11:51 AM, Stephen J. Turnbull <stephen@example.com>wrote:
 > > Nguyen Vu Hung writes:
 > >
 > >  > > No. It indicates the amount of time any one of the cores has
 > >  > > nothing to do.
 > >
 > >  > Is this a good design? I think no. I will replace OR with AND.
 > >  > Not every recently applications are SMP aware, and some never is.
 > >
 > > So?  That doesn't change the fact that some of the processors are
 > > doing almost no useful work!
 > 
 > I did mean "It indicates the amount of time any one of the cores
 > has nothing to do" does not make a good sense and it should be "It
 > indicates the amount of time *all the* cores has nothing to do".

Well, yes, I know that's what you meant.  It still doesn't make your
definition useful.  Your definition is biased upward.

 > > And multi-thread programming (like explicit heap management) is a
 > > waste of programmer skull-sweat in most server applications
 > 
 > I take graphicsmagick as an example.

Urk.  Examples are irrelevant to "most of the time".

And look, if you need the CPU, of course you need the CPU.  Nobody has
contested that.  But guess what?  The conventional statistic checked
when you are running graphicsmagick will show that you need CPU!  The
point is to find a number where when you need CPU it shows a high
load, and when you *don't* need CPU it shows you a *low* load.

 > > So, if your number says some of your processors are idle 99% of the
 > > time, and that bothers you,

 > I dual boot the dual Xeon box.

Well, OK, if you buy Intel, you obviously don't care at all how much
money you spend on CPU!<wink>

 > On Windows, I run Adobe PS3, which is using Adobe Camera Raw) to
 > convert hundreds of Nikon NEF files to JPEG. I really benefit from
 > SMP in this case.

Sure.  And that's the point of the precondition "it bothers you".  You
obviously like having your Windows do its thing really quickly so you
can get back to using a real OS as quickly as possible.  It evidently
*doesn't* bother you to have an 0.01 load level 99% of the time if for
the 1% (or whatever) of the time you've got a bunch of pix to process
the box screams.  In fact, in the case of this kind of image
processing it doesn't make sense to check /proc/uptime at all, since
what you are most interested in is peak-load performance.

But take those guys who are asking about MPUs.  They're obviously
interested in applications where spending too much money on CPUs is
bad, and I suppose there's a good chance they want to just buy enough
CPU to ensure that the data gets processed sooner or later (in CPU
cycles; in clock time probably a few seconds is the limit, although I
can easily imagine applications where it would be OK as long as you
catch up every day).  Then they might hope to push that ratio as high
as 25%.