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!
