On 7/5/2012 11:22, Orchid Win7 v1 wrote:
> (In spite of the fact that I'm actually using ALL the cores available.)

You're not, tho. Hyperthreading means you have like 1.5 cores for every 
"core". I assume you know what hyperthreading does. You could probably see a 
speed-up by running 5 copies of pov-ray instead of 4.

-- 
Darren New, San Diego CA, USA (PST)
   "Oh no! We're out of code juice!"
   "Don't panic. There's beans and filters
    in the cabinet."

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On 20/07/2012 12:45 AM, Darren New wrote:
> On 7/5/2012 11:22, Orchid Win7 v1 wrote:
>> (In spite of the fact that I'm actually using ALL the cores available.)
>
> You're not, tho. Hyperthreading means you have like 1.5 cores for every
> "core". I assume you know what hyperthreading does. You could probably
> see a speed-up by running 5 copies of pov-ray instead of 4.

As I understand it, hyperthreading allows you to schedule 2 threads on 
each core. The first thread gets all available resources. If any are 
unused, they are assigned to the second thread.

This means that if, say, one thread is using floating-point arithmetic 
and the other is using integer arithmetic, both threads run at nearly 
full speed. On the other hand, if both threads are using integer 
arithmetic, only one thread runs, and the other makes no progress. (At 
least, until the OS reschedules.)

Thus, I can believe that running two different applications might see a 
benefit. If they're performing different tasks, they probably use 
different execution unit types. But running two copies of the same 
application is highly unlikely to see any benefit - unless the 
application uses a really variable mix of instruction types...

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Le 20/07/2012 10:03, Invisible a écrit :
> On 20/07/2012 12:45 AM, Darren New wrote:
>> On 7/5/2012 11:22, Orchid Win7 v1 wrote:
>>> (In spite of the fact that I'm actually using ALL the cores available.)
>>
>> You're not, tho. Hyperthreading means you have like 1.5 cores for every
>> "core". I assume you know what hyperthreading does. You could probably
>> see a speed-up by running 5 copies of pov-ray instead of 4.

Well, personal measures about hyperthreading and povray 3.7 seems to
indicate that a HT core is rather between 1.2 and 1.25 core for povray
(see details and graph in povray.benchmarking). at least for the
benchmark scene.

> 
> As I understand it, hyperthreading allows you to schedule 2 threads on
> each core. The first thread gets all available resources. If any are
> unused, they are assigned to the second thread.

HT is: a second set of registers. Nothing more. No additional FPU or
fancy integer units.

> 
> This means that if, say, one thread is using floating-point arithmetic
> and the other is using integer arithmetic, both threads run at nearly
> full speed. On the other hand, if both threads are using integer
> arithmetic, only one thread runs, and the other makes no progress. (At
> least, until the OS reschedules.)

Well, it's more subtle, due to the Intel pipeline, but globally correct:
if they want the same resources at the same time, there is a contention
and the pipeline will rearrange them. The OS is usually unaware of such
issue: the granularity of the OS is far bigger than the small cycle in
the pipeline.

At best, operation of time 1 + another of time 1 could be done in 1 if
they do not use the same units at the same time... At worst it could be
2. Due to the pipeline splitting an instruction in multiple steps, it's
possible to interleave some steps in the empty slots of the first
thread-core.

> 
> Thus, I can believe that running two different applications might see a
> benefit. If they're performing different tasks, they probably use
> different execution unit types. But running two copies of the same
> application is highly unlikely to see any benefit - unless the
> application uses a really variable mix of instruction types...

Guess what, povray is not a single instruction!

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On 20/07/2012 12:20 AM, Darren New wrote:
> On 7/6/2012 10:36, clipka wrote:
>> Better yet, overwrite it with pseudorandom nonsense.
>
> On modern hard disks, this is useless. And by "modern" I mean pretty
> much anything that passed the 1GB boundary.

Care to elaborate on that?

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Le 20/07/2012 18:15, Orchid Win7 v1 nous fit lire :
> On 20/07/2012 12:20 AM, Darren New wrote:
>> On 7/6/2012 10:36, clipka wrote:
>>> Better yet, overwrite it with pseudorandom nonsense.
>>
>> On modern hard disks, this is useless. And by "modern" I mean pretty
>> much anything that passed the 1GB boundary.
> 
> Care to elaborate on that?
> 

Old fact: reading a hard disk by direct access to the disk, with some
electronic beam device... fine until the density and encoding on the
disk went into modern era.

Nowadays (and since most 1GB hard drive... quite old), its not possible
anymore. Writing 0 or random number is the same: the old data is not
recoverable.

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Am 20.07.2012 19:31, schrieb Le_Forgeron:
> Le 20/07/2012 18:15, Orchid Win7 v1 nous fit lire :
>> On 20/07/2012 12:20 AM, Darren New wrote:
>>> On 7/6/2012 10:36, clipka wrote:
>>>> Better yet, overwrite it with pseudorandom nonsense.
>>>
>>> On modern hard disks, this is useless. And by "modern" I mean pretty
>>> much anything that passed the 1GB boundary.
>>
>> Care to elaborate on that?
>>
>
> Old fact: reading a hard disk by direct access to the disk, with some
> electronic beam device... fine until the density and encoding on the
> disk went into modern era.
>
> Nowadays (and since most 1GB hard drive... quite old), its not possible
> anymore. Writing 0 or random number is the same: the old data is not
> recoverable.

Quiz: If you had highly sensitive data on your hard drive, and needed to 
erase it for sure - would you rather trust this alleged fact, or have 
the erasing software write random numbers just in case?

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Le 20/07/2012 19:46, clipka nous fit lire :
> 
> Quiz: If you had highly sensitive data on your hard drive, and needed to
> erase it for sure - would you rather trust this alleged fact, or have
> the erasing software write random numbers just in case?

If the data on drive was so sensitive, I would use chemistry first. Then
a bit of heavy hammer physic, and finally a good heat with partial
ionisation, at temperature far above the curie point.

Boiling HCl is probably enough, as a starter. (get ride of most iron &
steel). Wear a protective mask and operate under well vented condition.

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Am 20.07.2012 20:54, schrieb Le_Forgeron:
> Le 20/07/2012 19:46, clipka nous fit lire :
>>
>> Quiz: If you had highly sensitive data on your hard drive, and needed to
>> erase it for sure - would you rather trust this alleged fact, or have
>> the erasing software write random numbers just in case?
>
> If the data on drive was so sensitive, I would use chemistry first. Then
> a bit of heavy hammer physic, and finally a good heat with partial
> ionisation, at temperature far above the curie point.
>
> Boiling HCl is probably enough, as a starter. (get ride of most iron &
> steel). Wear a protective mask and operate under well vented condition.

Not recommended if you want to continue to use the hard drive though.

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On 7/20/2012 10:31, Le_Forgeron wrote:
> Nowadays (and since most 1GB hard drive... quite old), its not possible
> anymore. Writing 0 or random number is the same: the old data is not
> recoverable.

This. Plus, if it's an SSD or has flash backup, you can write it all you 
want and unless you rewrite the entire drive multiple times, you're not 
guaranteed to get rid of the junk.

-- 
Darren New, San Diego CA, USA (PST)
   "Oh no! We're out of code juice!"
   "Don't panic. There's beans and filters
    in the cabinet."

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On 7/20/2012 13:22, clipka wrote:
> Am 20.07.2012 20:54, schrieb Le_Forgeron:
>> Le 20/07/2012 19:46, clipka nous fit lire :
>>>
>>> Quiz: If you had highly sensitive data on your hard drive, and needed to
>>> erase it for sure - would you rather trust this alleged fact, or have
>>> the erasing software write random numbers just in case?
>>
>> If the data on drive was so sensitive, I would use chemistry first. Then
>> a bit of heavy hammer physic, and finally a good heat with partial
>> ionisation, at temperature far above the curie point.
>>
>> Boiling HCl is probably enough, as a starter. (get ride of most iron &
>> steel). Wear a protective mask and operate under well vented condition.
>
> Not recommended if you want to continue to use the hard drive though.

If it's not sensitive enough to pay to replace the drive, it's not sensitive 
enough to worry about whether you're erased with zeros or with random data.

-- 
Darren New, San Diego CA, USA (PST)
   "Oh no! We're out of code juice!"
   "Don't panic. There's beans and filters
    in the cabinet."

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