Re: [gentoo-user] Re: aligning SSD partitions

[Dale <rdalek1967@gmail.com>]

Nicolas Sebrecht wrote:
> The 06/09/12, Dale wrote:
>
>> I do get it.  I CLEARED #1 and #2, there is no usage of #3 and #4 is not
>> large enough here to matter.  So, it is left with #5. 
>>
>> See the point?  The test was a NORMAL emerge with portages work
>> directory on tmpfs and a NORMAL emerge with portages work directory on
>> disk and compare the results.  The test resulted in little if any
>> difference. 
>>
>> If I ran the test and did not clear the cache, then I would expect
>> skewed results because after the first emerge, some files would be
>> cached in ram and the drive would not be used.  If you clear the cache,
>> then it has to take the same steps regardless of whether it was run
>> first, second or third time. 
> What you want to measure is the difference of times required by emerge
> whether you use a real disk or tmpfs as backend.
>
> What you would expect is a difference because a disk is much slower than
> RAM.
>
> What you see is no difference. You won't conclude that disk is as fast
> as RAM, right? Can you explain why you don't see much difference? No.
>
> Here is the explanation: if you have enough RAM, the emerge rapidity
> will NOT rely on the disk rapidity whatever storage backend you use. It
> will only rely on the RAM rapidity because of the kernel cache.
>
> Now, pretending that whatever backend you use (real disk or tmpfs) never
> changes the emerge time is WRONG because of the persistence strategy
> used by the kernel for the kernel cache.
>
> When having lot of RAM like you have, the persistence strategy of the
> kernel cache is NEVER raised in the process.
>
> This is exactly what your tests demonstrate demonstrate: if you have
> enough RAM, the persistence strategy of kernel cache is not raised, so
> everything happens in RAM, so the emerge times do not differ.
>

The end result is this, it doesn't matter if portage's work directory is
on tmpfs or not.  You just concluded that yourself which is what I have
been saying.  It doesn't matter WHY it doesn't matter, it just matters
that it DOESN'T matter.  It takes just as long on a system with
portage's work directory on tmpfs as it does on tmpfs.  Very little
difference at all.  The variance I had was minimal at best.  It was
basically seconds of difference not minutes.

I might add, I got the same results on my older system which has a LOT
less ram.  I think it only has 2Gbs or so. 

Dale

:-)  :-) 

-- 
I am only responsible for what I said ... Not for what you understood or how you interpreted my words!