Poor performance of i7-7700 HQ processors [SOLVED]

$nake · 2017-08-19 19:50:59

I recently changed my Toshiba Satellite L70-B-12H with i7-4700 HQ processors, for an ASUS GL553VD with i7-7700 HQ processors.
I perform some numerical analysis with a program written in C/C++ interfaced to GNU Octave with Mex; it uses parallel threads thanks to Open MP.
I am disapointed to see that my new computer, with the better processors, is up to 2 times slower than the older, with the lesser processors, to perform the same task. I checked the basics: `grep "cpu MHz" /proc/cpuinfo` shows that all 8 CPUs are in use, and that they all go up to 3.40 GHz. Although the i7-7700 HQ are supposed to be able to go up to 3.80 GHz, I think this cannot be when all 8 are in use; anyway this cannot account for the lesser performance since the i7-4700 HQ are themselves limited to 3.40 GHz.

My question: is there anything obvious that could explain the lesser performance with better hardware? Any workaround?

Most important differences I can think of:

[it]the older computer had 16 GB of RAM[/it], against only 8 GB for the newer. The task at hand requires easily 2.4 GB, so memory might be a factor. But would this explain such a difference?

Graphic cards are different, but can a simple C/C++ program benefit from GPU anyway? and again, the new one is supposed to be better, I checked that it is working with the proprietary nvidia drivers.

edit: changed 7400 to 4700

Last edited by $nake (2017-11-17 09:14:41)

Slithery · 2017-08-19 19:59:38

According to Intel there is no i7-7400...
https://ark.intel.com/search?q=i7-7400

What processor is it really?

Edit - I guess you meant i7-4700HQ.
Those processors look fairly comparable (apart from the newer IPC) - https://ark.intel.com/compare/97185,75116
Could it possibly be a memory bandwidth issue if you had 2 or more sticks of RAM in the older machine but only 1 in the newer?
Have you configured the power-saving differently on each laptop?

Last edited by Slithery (2017-08-19 20:17:41)

brebs · 2017-08-19 20:54:53

I would speculate that it could be the Intel microcode working around CPU bugs, e.g. hyper-threading bug.

I suggest comparing with/without microcode loaded.

R00KIE · 2017-08-19 21:22:22

I would also suggest keeping an eye on temperatures, there is always the possibility that the cpu is throttling due to high temperatures.

$nake · 2017-08-19 21:38:36

Thanks for the reply, it is indeed i7-4700HQ.
I would be surprised that the difference comes from the memory only, but again this seems the main difference between the two setting.

I'll have a look at this "microcode" issue and report back.

As for the temperature, I should have mentioned that I monitored it during the task, and rarely going higher than 70°C. For the sake of completeness, I must say that in many trials, I have seen a couple of CPU throttling events in dmesg, but in most trials the performance was poor with no mention of CPU throttling.

$nake · 2017-08-19 23:33:49

I am not entirely sure what is this "microcode" and how to load it. Following the wiki I installed intel-ucode and added the initrd /intel-ucode.img in my boot config. After reboot I check

$ dmesg | grep microcode
[    0.000000] microcode: microcode updated early to revision 0x5e, date = 2017-04-06
[    1.520152] microcode: sig=0x906e9, pf=0x20, revision=0x5e
[    1.520387] microcode: Microcode Update Driver: v2.2.

so I guess microcode is now loaded. However, this did not change the performances on my task.

$nake · 2017-11-17 09:13:11

For the record: the lesser performance by the supposedly better computer came indeed from a _memory_ issue. However, it was not in term of absolute use of memory, but because of _memory bandwidth_ (in my understanding, how fast can data go in and out of RAM). On the Toshiba, I had "dual channel" memory, that is the two memory sticks could be accessed in parallel. I added a memory stick to the ASUS, and I recovered the expected slightly better performances.

Last edited by $nake (2018-10-05 12:43:57)

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#1 2017-08-19 19:50:59

Poor performance of i7-7700 HQ processors [SOLVED]

#2 2017-08-19 19:59:38

Re: Poor performance of i7-7700 HQ processors [SOLVED]

#3 2017-08-19 20:54:53

Re: Poor performance of i7-7700 HQ processors [SOLVED]

#4 2017-08-19 21:22:22

Re: Poor performance of i7-7700 HQ processors [SOLVED]

#5 2017-08-19 21:38:36

Re: Poor performance of i7-7700 HQ processors [SOLVED]

#6 2017-08-19 23:33:49

Re: Poor performance of i7-7700 HQ processors [SOLVED]

#7 2017-11-17 09:13:11

Re: Poor performance of i7-7700 HQ processors [SOLVED]

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