Re: AMD Shanghai versus Intel Nehalem

On 5/13/09 11:21 PM, "Arjen van der Meijden" <acmmailing(at)tweakers(dot)net>
wrote:

> On 13-5-2009 20:39 Scott Carey wrote:
>> Excellent! That is a pretty huge boost. I'm curious which aspects of this
>> new architecture helped the most. For Postgres, the following would seem
>> the most relevant:
>> 1. Shared L3 cache per processors -- more efficient shared datastructure
>> access.
>> 2. Faster atomic operations -- CompareAndSwap, etc are much faster.
>> 3. Faster cache coherency.
>> 4. Lower latency RAM with more overall bandwidth (Opteron style).
>
> Apart from that, it has a newer debian (and thus kernel/glibc) and a
> slightly less constraining IO which may help as well.
>
>> Can you do a quick and dirty memory bandwidth test? (assuming linux)
>> On the older X5355 machine and the newer E5540, try:
>> /sbin/hdparm -T /dev/sd<device>
>
> It is in use, so the results may not be so good, this is the best I got
> on our dual X5355:
> Timing cached reads: 6314 MB in 2.00 seconds = 3159.08 MB/sec
>
> But this is the best I got for a (also in use) Dual E5450 we have:
> Timing cached reads: 13158 MB in 2.00 seconds = 6587.11 MB/sec
>
> And here the best for the (idle) E5540:
> Timing cached reads: 16494 MB in 2.00 seconds = 8256.27 MB/sec
>
> These numbers are with hdparm v8.9

Thanks!

My numbers were with hdparm 6.6 (Centos 5.3) -- so they aren't directly
comparable.
FYI When my systems are in use, the results are typically 50% to 75% of the
idle scores.

But, yours probably are roughly comparable to each other -- you're getting
more than 2x the memory bandwidth between those systems. Without knowing
the exact chipset and RAM configurations, this is definitely a factor in the
performance difference at higher concurrency.

>
> Best regards,
>
> Arjen
>