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Old 2016-09-12, 09:59   #1
primecrusader
 
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Default How much will hyper threading help

I am thinking of buying a used IBM SERVER X3650 (To only run prime 95) with a Xeon E5420 that doesn't have hyper-threading and room for two CPUs (I will be buying a second CPU) and I was wondering if it would be worth it to buy two different CPUs with hyper-threading instead of just buying a second Xeon E5420 that doesn't have hyper-threading since the CPUs are quite cheap if I buy used ones off the internet.
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Old 2016-09-12, 10:08   #2
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The amount of assistance that the extra SMT "cores" gives can vary from negligibly positive (a few % at most) to negligibly negative (also a few %). IMO it is not worth the bother to use SMT with P95. But that doesn't mean other tasks can't make good use of the additional resources. However be aware that the OS has no control over the relative priorities for two threads that share a single execution unit, so with P95 running it can make other higher priority tasks slower if you have SMT enabled.
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Old 2016-09-12, 10:43   #3
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That is a really old CPU. You're probably better off building a cheap Skylake i3
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Old 2016-09-12, 13:20   #4
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Quote:
Originally Posted by axn View Post
That is a really old CPU. You're probably better off building a cheap Skylake i3
Agreed that CPU is way too old. A skylake i5 will get twice the performance of both CPUs together at a quarter or less the power.
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Old 2016-09-12, 14:16   #5
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Quote:
Originally Posted by primecrusader View Post
I am thinking of buying a used IBM SERVER X3650 (To only run prime 95) with a Xeon E5420 that doesn't have hyper-threading and room for two CPUs (I will be buying a second CPU) and I was wondering if it would be worth it to buy two different CPUs with hyper-threading instead of just buying a second Xeon E5420 that doesn't have hyper-threading since the CPUs are quite cheap if I buy used ones off the internet.
I'll agree with some of the comments that these CPUs probably won't be terribly useful for Prime95. A server is going to use a lot of power and for a CPU of that vintage it may not be worthwhile.

I have a couple old Proliant servers of that vintage (some with Xeon 51xx and a couple with Xeon 54xx) that I don't bother running Prime95 on. I would shut them down entirely but one of them is just there as a redundant physical box in a collocation "just in case".

The memory for those is limited to DDR2 @ 667 MHz so that alone means it'll go fairly slow.

If you're dead set on it though, if you can pick up a (matching) pair of whatever the fastest speed chips you can, go for it. The key there is "matching" CPUs. In the real world it may not matter terribly much, but servers do tend to work best when both CPUs have the same stepping. The latest BIOS will ensure the latest microcode is present but having CPUs at the same stepping levels really helps ensure it's all good.

If you merely picked up another E5420 it probably wouldn't match. I've looked on eBay before for upgrade CPUs for old servers and you should have no problem finding listings for matching pairs that were pulled out of old equipment.

FYI, if you need any memory for these, I think I still have a collection of DDR2 ECC modules at the 1GB size. I'm pretty sure I have some 2GB and maybe even a couple at 4GB. The machines they used to live in have long been recycled, but I'm a packrat and grabbed the memory and anything else useful before they went off the great recycling plant in the sky.
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Old 2016-09-12, 14:23   #6
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Quote:
Originally Posted by primecrusader View Post
... would be worth it to buy two different CPUs with hyper-threading instead of just buying a second Xeon E5420 that doesn't have hyper-threading...
By the way, that had me wondering...what LGA 771 server CPU supports HT, and I looked it up. You'd have to go back to the Xeon 50xx models with only dual-core if you wanted to have hyper-threading. Don't do it. *Real* quad-core CPUs are MUCH better than HT dual-core CPUs. Not to mention the other improvements from Dempsey to Harpertown (65nm to 45nm, dual-to-quad, "Netburst" to "Penryn", "Willamette" core to "Wolfdale" core, etc.
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Old 2016-09-15, 17:11   #7
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Besides all the excellent reasons given above, have you ever heard one of these things?
Generally, these "pizza box" servers have LOTS of tiny fans to fit in that form factor
and they run at extremely high RPMs making them SCHREECH and SCREAM !!
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Old 2016-09-16, 01:51   #8
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Quote:
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Besides all the excellent reasons given above, have you ever heard one of these things?
Generally, these "pizza box" servers have LOTS of tiny fans to fit in that form factor
and they run at extremely high RPMs making them SCHREECH and SCREAM !!
Very much so. Whenever I get a new one, I fire it up on my desk first after installing whatever options, setup the management IP settings, etc. I draw some glares and comments each and every time about the "jet engine" on my desk.

Meanwhile, I was curious about upgrading the CPUs on the Primenet server. Currently it's a pair of X5550's which aren't bad, dual 4-core with HT. But that server supports the X5600 models and it might be nice to get a pair of hex-core chips.

Well, turns out you can actually buy an entire HP Proliant server (minus hard drives) on eBay for between 100-200, with a little memory as well. Either a DL360 G6 or G7 (which are pretty similar).

Point being, why spend something like 20-50 bucks on a matched pair of 54xx CPUs when you can just get a new server with matching 56xx for still a pretty cheap price? The thing there being you need at least one SAS drive, but you can pick those up cheap too, or just a blank caddy and get a decent SSD SAS.

I'm thinking it might be nice to pick up a decent used G7 server for Primenet... sometimes when I'm running my more involved queries in SQL, I can peg the CPU for a few seconds at a time so I find that I try to limit the more in-depth stuff out of deference to the needs of Primenet and the public.

I bet similarly cheap deals on Dell and IBM 1U servers exist of that same CPU vintage.
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