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Thread: Number of cores, "SUSE"

  1. #1
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    Default Number of cores, "SUSE"

    Hi!
    I have a question first, this whit the number of cores/treads and the hysteria:

    Oh there is a lot of blogs, - test on new hardware. But I have also a question and would like to check with forum if I..

    The command top sending (On my old server in the basement a AMD Athlon II X4 630(4 cores/treads) never exceed 4.0 in load except when I running an backup(I have 1GB lan):
    Code:
    top - 15:05:22 up 1 day,  1:46,  2 users,  load average: 4,45, 3,96, 3,20
    Tasks: 192 total,   1 running, 191 sleeping,   0 stopped,   0 zombie
    %Cpu(s):  1,1 us,  4,8 sy,  0,6 ni, 23,8 id, 63,7 wa,  0,0 hi,  6,0 si,  0,0 st
    KiB Mem:  12045016 total, 11772764 used,   272252 free,     3188 buffers
    KiB Swap:  2103292 total,        0 used,  2103292 free.  8628420 cached Mem
    
      PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND    
     3337 root      20   0 4291420 2,668g 2,620g S 12,25 23,22 186:03.34 VBoxHeadl+ 
    20133 root      20   0  259948   7216   5248 S 4,636 0,060   2:27.66 iftop      
     1862 root      20   0       0      0      0 D 3,311 0,000   2:32.24 nfsd       
     1864 root      20   0       0      0      0 D 3,311 0,000   3:32.81 nfsd       
     1861 root      20   0       0      0      0 D 2,980 0,000   2:30.24 nfsd       
     1863 root      20   0       0      0      0 D 2,318 0,000   2:48.05 nfsd       
    20968 root      20   0   15360   2616   2072 R 0,662 0,022   0:00.37 top
    On my main pc (AMD A8-3850 APU 4 cores/treads) receiving on a e-sata mechanical disk.
    top - 15:02:39 up 1:59, 3 users, load average: 3,63, 3,70, 3,32
    Tasks: 263 total, 3 running, 259 sleeping, 0 stopped, 1 zombie
    %Cpu(s): 17,9 us, 9,7 sy, 0,0 ni, 38,5 id, 25,5 wa, 0,0 hi, 8,5 si, 0,0 st
    KiB Mem: 11782244 total, 11630944 used, 151300 free, 39952 buffers
    KiB Swap: 2104316 total, 0 used, 2104316 free. 10254940 cached Mem

    PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    11752 xxxxx 20 0 39092 16096 1476 S 48,84 0,137 21:24.93 rsync
    11731 xxxxx 20 0 39456 18016 3200 D 45,51 0,153 19:51.63 rsync
    12861 root 0 -20 0 0 0 S 30,90 0,000 1:40.91 kworker/3+
    43 root 20 0 0 0 0 S 3,987 0,000 1:37.93 kswapd0
    12777 root 20 0 0 0 0 D 2,658 0,000 0:05.53 kworker/u+
    9205 root 20 0 0 0 0 R 1,993 0,000 0:49.98 jbd2/sdf1+
    The question is, - 4 cores and when the load is not step over 4.0 I'm still in the game? I would like to buy a Porsche but do I need to?

    ROI, attach a picture from 2002 from middle east. The computer is in my private workshop home here running TW 32 bit.

    regards
    I'm shameless like others in the forum -was I to any help or made sense? If yes: click the on the star below to the left. Written whit a ;-) in my eye.

  2. #2

    Default Re: Number of cores, "SUSE"

    On 2017-09-05, jonte1 <jonte1@no-mx.forums.microfocus.com> wrote:
    > <SNIP>
    > Code:
    > --------------------
    > top - 15:05:22 up 1 day, 1:46, 2 users, load average: 4,45, 3,96, 3,20
    > Tasks: 192 total, 1 running, 191 sleeping, 0 stopped, 0 zombie
    > %Cpu(s): 1,1 us, 4,8 sy, 0,6 ni, 23,8 id, 63,7 wa, 0,0 hi, 6,0 si, 0,0 st
    > KiB Mem: 12045016 total, 11772764 used, 272252 free, 3188 buffers
    > KiB Swap: 2103292 total, 0 used, 2103292 free. 8628420 cached Mem
    >
    > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    > 3337 root 20 0 4291420 2,668g 2,620g S 12,25 23,22 186:03.34 VBoxHeadl+
    > 20133 root 20 0 259948 7216 5248 S 4,636 0,060 2:27.66 iftop
    > 1862 root 20 0 0 0 0 D 3,311 0,000 2:32.24 nfsd
    > 1864 root 20 0 0 0 0 D 3,311 0,000 3:32.81 nfsd
    > 1861 root 20 0 0 0 0 D 2,980 0,000 2:30.24 nfsd
    > 1863 root 20 0 0 0 0 D 2,318 0,000 2:48.05 nfsd
    > 20968 root 20 0 15360 2616 2072 R 0,662 0,022 0:00.37 top
    > --------------------
    >
    > <SNIP>
    >
    > The question is, - 4 cores and when the load is not step over 4.0 I'm
    > still in the game? I would like to buy a Porsche but do I need to?


    I don't understand your question. If you want to see the thread load per-core in `top', you have to press 1. There's no
    point increasing your core count if your speed-critical program is not explicitly coded to be CPU multithreaded
    otherwise it will still use just a single thread however many logical threads you have available. The correspondence
    between logical threads and cores is not necessarily 1:1 (as it with AMD cores) since Intel chips distribute two threads
    per core.

    However execution threads need not correspond with the theoretical logical maximum. Some programmers even subscribe to
    the belief to the number of executation threads should correspond to the number of theoretical maximum plus two. My
    opinion is that is rubbish and there is little/no benefit exceeding the theoretical maximum and more often than not,
    doing so is usually harmful to performance.

    Bear in mind even for multithreaded code, a doubling of maximum threads can rarely reduce execution time to half (with
    the notable exception of going from 1 to 2 threads). It depends on the operation and the total thread count since there
    are diminishing returns on increasing numbers of threads, and within the range of CPUs used on desktop PCs you're doing
    well if the the execution time is reduced by ~30% per doubling of maximum thread counts.

  3. #3
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    Default Re: Number of cores, "SUSE"

    Today's Intel and AMD x86/x64 processors are SMP processors.

    This generally means that no matter whether your app is written multi-threaded or not, execution will be across all processors (and cores) according to the processors's own internal instructions.

    But, if your application is specifically written to be multi-threaded, then more complex calculations can be performed faster by improved parallelism.

    What this generally means is that you're probably not going to get desired results unless your benchmarking app (or other software) over-rides what is done automatically and does things like assigning processor affinities.

    Note that this is different than for example what I've observed on ARM processors which is one major reason why every app might run full screen by default. To support screen splitting (apps running side by side on the screen) and multi-tasking, each app is running in its own core.

    And,
    If you're talking about GPU processing and rendering, then that's another architecture where you have a layer of virtual cores on top of your real, physical cores vastly increasing parallelism potential compared to CPUs which still utilize SIMD(Intel) which are specialized instruction sets for certain high performance tasks.

    So, if you're going to benchmark, you'll need to first understand what you're testing(unless you're only interested in default settings and bottom line numbers).

    HTH,
    TSU
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  4. #4

    Default Re: Number of cores, "SUSE"

    On 2017-09-06, tsu2 <tsu2@no-mx.forums.microfocus.com> wrote:
    >
    > Today's Intel and AMD x86/x64 processors are SMP processors.
    >
    > This generally means that no matter whether your app is written
    > multi-threaded or not, execution will be across all processors (and
    > cores) according to the processors's own internal instructions.


    Ahh... if only that were true, it would save me a lot of work!

    In practice without explicit multithreading code (e.g. using std::thread or pthreads), at best a single executable is
    distributed across two threads with anything beyond a non-trivial CPU-load. The problem is that the fastest caches (L1
    and L2) cannot be across cores and as a result SMP factors rarely exceed 1.2X-1.4X increases in speed whatever the core
    count. In my opinion therefore, the SMP environment is ideal for running different programs at the same time but a poor
    substitute for multithreading.

  5. #5
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    Default Re: Number of cores, "SUSE"

    A couple of things:
    - When writing posts, please be clear about what your issue is.
    - It's openSUSE. SUSE is a different beast
    - On 64-bit systems, run 64-bit openSUSE. The 32-bit TW is still there, but less and less people are using it. Count on it disappearing
    ° Appreciate my reply? Click the star and let me know why.

    ° Perfection is not gonna happen. No way.

    http://en.opensuse.org/User:Knurpht
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  6. #6
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    Default Re: Number of cores, "SUSE"

    Quote Originally Posted by flymail View Post
    On 2017-09-06, tsu2 <tsu2@no-mx.forums.microfocus.com> wrote:
    >
    > Today's Intel and AMD x86/x64 processors are SMP processors.
    >
    > This generally means that no matter whether your app is written
    > multi-threaded or not, execution will be across all processors (and
    > cores) according to the processors's own internal instructions.


    Ahh... if only that were true, it would save me a lot of work!

    In practice without explicit multithreading code (e.g. using std::thread or pthreads), at best a single executable is
    distributed across two threads with anything beyond a non-trivial CPU-load. The problem is that the fastest caches (L1
    and L2) cannot be across cores and as a result SMP factors rarely exceed 1.2X-1.4X increases in speed whatever the core
    count. In my opinion therefore, the SMP environment is ideal for running different programs at the same time but a poor
    substitute for multithreading.
    True, one of the factors affecting execution is are the L1 and L2 caches, and then if available to specific or all cores of a processor. IIRC the latest AMD processor is supposed to do something revolutionary to improve this.

    TSU
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  7. #7
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    Default Re: Number of cores, "SUSE"

    Quote Originally Posted by Knurpht View Post
    A couple of things:
    - When writing posts, please be clear about what your issue is.
    - It's openSUSE. SUSE is a different beast
    - On 64-bit systems, run 64-bit openSUSE. The 32-bit TW is still there, but less and less people are using it. Count on it disappearing
    Good general advice, but this thread is more of a hardware topic, not specific to software at any level except at lowest levels.

    TSU
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  8. #8
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    Default Re: Number of cores, "SUSE"

    What I read from the two "top" outputs is, that the cpu's are not fully loaded ("id"le values of 23.8% and 38.5%) and the system is waiting for I/O's to complete ("wa"it values of 63.7% and 25.5%).
    IMHO more cpu cores do not make a lot of sense with this workload. Everything else needs further investigation about the bottlenecks and more info about the workload(s).

    Hendrik

  9. #9
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    Default Re: Number of cores, "SUSE"

    Quote Originally Posted by tsu2 View Post
    Good general advice, but this thread is more of a hardware topic, not specific to software at any level except at lowest levels.

    TSU
    It isn't. It is General Chitchat. Everybody can say what (s)he wants (as long as it abides to the T&C). Nobody has to take anything here serious.
    Henk van Velden

  10. #10

    Default Re: Number of cores, "SUSE"

    On 2017-09-06, tsu2 <tsu2@no-mx.forums.microfocus.com> wrote:
    > True, one of the factors affecting execution is are the L1 and L2
    > caches, and then if available to specific or all cores of a processor.


    L1 and L2 caches are core-confined whereas L3 is pooled across cores. My experience prefetching data to L3 caches is
    very limited but the L3 latency is so poor that from little testing I've done, I've found prefetches to L3 largely
    homeopathic for performance.

    > IIRC the latest AMD processor is supposed to do something revolutionary
    > to improve this.


    That sounds exciting! Do you have a reference for this?

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