L2 Cache – Is it worth it????

[DaveNamou]

I was looking at some systems to recommend to a client.
My main goal is to make sure the server has 2 Processors, 2GB RAM and a RAID controller with RAID1 or RAID5.

I don’t want more than 2 processors cause NT doesn’t utilize the 3rd and 4th processors efficiently.

After going online and looking at some IBM xSeries servers (IBM is the client’s choice, not mine), I started wondering how important L2 cache is and is it worth it’s money. I configured 6 servers, all with the exact same specs except for the processor.
(1) X342 - $6120=Duel PIII 1000MHz – 256 L2
(2) X342 - $6420=Duel PIII 1130MHz – 512 L2
(3) X342 - $6720=Duel PIII 1260MHz – 512 L2
(4) X350 - $8938=Duel PIII Xeon 700MHz – 1024 L2
(5) X350 - $11,558=Duel PIII Xeon 700MHz - 2048 L2
(6) X350 - $17,868=Duel PIII Xeon 900MHz – 2048 L2

Obviously server1 and server2 are out of the question. Cost wise, server3 is better than both.

So, my main questions are…
* Is it true that L2 Cache is only beneficial if you’re running 1 or 2 apps? That way those apps instructions are always cached in L1 or L2.
* Wouldn’t the 3rd server be faster than the 4th and 5th server? The speed is near double! I know Xeon processors are supposed to be faster, but I thought the main difference between PIII and PIII Xeon was the L2 cache…which leads me back to the question of is L2 cache that beneficial.
* Server4 and server5 are identical except for L2. How many more users can I squeeze on there with that extra L2? For example, if server4 could hold 30 people, how many can server5 handle with that extra 1MB of L2 Cache?

Any input is greatly appreciated!! Thanks!

Dave Namou, MCSE CCEA

 

[jimbopalmer]

Disclaimer: All my computing is with Oracle database on Unix and with Macs. This should not matter, but I put it up here so you know.

Oracle on Unix: 36 k cache to 256k cache (on four CPUs) was a 2.5 to 1 speed up with 125 users

256k cache to 1 meg cache was a 3 to 1 speed up (on 4 CPUs) with 200 users

1 meg to 4 meg cache (on 8 CPUs) was a 2 to 1 speed up with 250 users

Mac: 512k Seti@home unit is 32 hours, 1 meg SETI@home unit is 23 hours. the 1 meg much more cheerfully multi tasks as the odds are that the other programs did not flush from cache.


one typo you made is in fact the reason L2 cache works SO well for miltiprocessing Dual CPUs do not duel for L2 cache, they each have their own, but they do duel for main memory, which is already 15 times slower than ONE CPU. I tried to remain child-like, all I acheived was childish.