questions on multiple thread programming

This is a discussion on questions on multiple thread programming within the C Programming forums, part of the General Programming Boards category; I perhaps have to resort to multiple thread programming to reduce computational time. I am now studying how to use ...

  1. #1
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    questions on multiple thread programming

    I perhaps have to resort to multiple thread programming to reduce computational time. I am now studying how to use POSIX library.
    I can access a cluster with 8 CPUs, each of which has one core. I was wondering how many threads to create would get approximately best time performance on my cluster? Is it the same number of CPUs? If I am using multiple thread library like POSIX, will the library take care of which thread run on which CPU or do I have to specify this in my code?

    Thanks!

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    To get the best performance, create one thread per core. The library (or more specifically, the OS scheduler) will take care of which thread runs on which core. You don't need to worry about this.

  3. #3
    CSharpener vart's Avatar
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    Quote Originally Posted by bithub View Post
    To get the best performance, create one thread per core. The library (or more specifically, the OS scheduler) will take care of which thread runs on which core. You don't need to worry about this.
    I would say 1 worker thread per CPU

    plus you can have several IO threads for example which will most of the time spend in waiting state while io operation is been completed
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    I would say 1 worker thread per CPU
    Can you explain why you would use 1 thread per CPU instead of 1 thread per core? To software applications, there is no difference.

    plus you can have several IO threads for example which will most of the time spend in waiting state while io operation is been completed
    Why would you create several threads to wait for IO? For the best performance, async IO is the best way to go.

  5. #5
    CSharpener vart's Avatar
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    Quote Originally Posted by bithub View Post
    Can you explain why you would use 1 thread per CPU instead of 1 thread per core? To software applications, there is no difference.

    Why would you create several threads to wait for IO? For the best performance, async IO is the best way to go.
    by cpu I mean core

    several IO? because you can have a logger thread writign logs to file,
    db connection threads - requestion data from remote db server
    sochet thread - processing some network connection etc...

    it is too complicated to put all these task on one io thread
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  6. #6
    Registered User Codeplug's Avatar
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    >> I can access a cluster with 8 CPUs, each of which has one core.
    Multi-threading is for a single machine. For distributed-parallel programming you'll need something like MPI. Unless you're running a distributed OS providing SSI like openMosix.

    gg

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    Thanks!
    Yes I remember people called my server "cluster". But how to check if it is distributed system and running a distributed OS providing SSI? And which shall I use, multi-threading or distributed-parallel programming?

    Here is the info of my server from uname:
    Linux 2.6.9-78.0.8.ELsmp #1 SMP Wed Nov 19 19:42:38 EST 2008 x86_64 x86_64 x86_64 GNU/Linux
    And also info from cat /proc/cpuinfo
    processor : 0
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Xeon(TM) MP CPU 3.66GHz
    stepping : 1
    cpu MHz : 3657.792
    cache size : 1024 KB
    physical id : 0
    siblings : 2
    core id : 0
    cpu cores : 1
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl est tm2 cid cx16 xtpr
    bogomips : 7321.81
    clflush size : 64
    cache_alignment : 128
    address sizes : 40 bits physical, 48 bits virtual
    power management:

    processor : 1
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Xeon(TM) MP CPU 3.66GHz
    stepping : 1
    cpu MHz : 3657.792
    cache size : 1024 KB
    physical id : 4
    siblings : 2
    core id : 4
    cpu cores : 1
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl est tm2 cid cx16 xtpr
    bogomips : 7315.15
    clflush size : 64
    cache_alignment : 128
    address sizes : 40 bits physical, 48 bits virtual
    power management:

    processor : 2
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Xeon(TM) MP CPU 3.66GHz
    stepping : 1
    cpu MHz : 3657.792
    cache size : 1024 KB
    physical id : 3
    siblings : 2
    core id : 3
    cpu cores : 1
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl est tm2 cid cx16 xtpr
    bogomips : 7315.02
    clflush size : 64
    cache_alignment : 128
    address sizes : 40 bits physical, 48 bits virtual
    power management:

    processor : 3
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Xeon(TM) MP CPU 3.66GHz
    stepping : 1
    cpu MHz : 3657.792
    cache size : 1024 KB
    physical id : 7
    siblings : 2
    core id : 7
    cpu cores : 1
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl est tm2 cid cx16 xtpr
    bogomips : 7315.10
    clflush size : 64
    cache_alignment : 128
    address sizes : 40 bits physical, 48 bits virtual
    power management:

    processor : 4
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Xeon(TM) MP CPU 3.66GHz
    stepping : 1
    cpu MHz : 3657.792
    cache size : 1024 KB
    physical id : 0
    siblings : 2
    core id : 0
    cpu cores : 1
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl est tm2 cid cx16 xtpr
    bogomips : 7315.04
    clflush size : 64
    cache_alignment : 128
    address sizes : 40 bits physical, 48 bits virtual
    power management:

    processor : 5
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Xeon(TM) MP CPU 3.66GHz
    stepping : 1
    cpu MHz : 3657.792
    cache size : 1024 KB
    physical id : 4
    siblings : 2
    core id : 4
    cpu cores : 1
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl est tm2 cid cx16 xtpr
    bogomips : 7314.70
    clflush size : 64
    cache_alignment : 128
    address sizes : 40 bits physical, 48 bits virtual
    power management:

    processor : 6
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Xeon(TM) MP CPU 3.66GHz
    stepping : 1
    cpu MHz : 3657.792
    cache size : 1024 KB
    physical id : 3
    siblings : 2
    core id : 3
    cpu cores : 1
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl est tm2 cid cx16 xtpr
    bogomips : 7314.99
    clflush size : 64
    cache_alignment : 128
    address sizes : 40 bits physical, 48 bits virtual
    power management:

    processor : 7
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Xeon(TM) MP CPU 3.66GHz
    stepping : 1
    cpu MHz : 3657.792
    cache size : 1024 KB
    physical id : 7
    siblings : 2
    core id : 7
    cpu cores : 1
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl est tm2 cid cx16 xtpr
    bogomips : 7315.06
    clflush size : 64
    cache_alignment : 128
    address sizes : 40 bits physical, 48 bits virtual
    power management:

  8. #8
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    That is one machine for all intents and purposes.

    --
    Mats
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    Please don't PM me for help - and no, I don't do help over instant messengers.

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    Hi Matsp,
    Thanks!
    From where did you tell it is not a distribution system? Does "cluster" only refer to distributed system?
    So I should stick to multi-threading programming?

  10. #10
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    Quote Originally Posted by lehe View Post
    Hi Matsp,
    Thanks!
    From where did you tell it is not a distribution system? Does "cluster" only refer to distributed system?
    So I should stick to multi-threading programming?
    A cluster/distributed system will not show that you have 8 cores in /proc/cpuinfo. It will only show the cores of THAT system, which will be one or two perhaps.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  11. #11
    Registered User Codeplug's Avatar
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    The term "cluster" implies more than one physical machine (PC). You have a single machine with 8 cores, so Posix "multi-threading" (with pthreads or processes) is appropriate in this case.

    >> I was wondering how many threads to create would get approximately best time performance on my cluster?
    The answer can depend on what you're doing, but a typical answer is one thread per core - as bithub and vart mentioned.

    >> will the library take care of which thread run on which CPU or do I have to specify this in my code?
    The typical answer is that you let your OS/library take care of this for you.

    gg

  12. #12
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    Quote Originally Posted by Codeplug View Post
    >> will the library take care of which thread run on which CPU or do I have to specify this in my code?
    The typical answer is that you let your OS/library take care of this for you.
    And unless you have SPECIFIC knowledge from understanding the problem nature, the OS in question and processors in question, it is nearly always a waste of time to try to improve on what the OS/library does.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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