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Re: Whats' the proper senario of par-map? (Was Re: bug#13188: par-map ca
From: |
Ludovic Courtès |
Subject: |
Re: Whats' the proper senario of par-map? (Was Re: bug#13188: par-map causes VM stack overflow) |
Date: |
Thu, 28 Mar 2013 21:07:12 +0100 |
User-agent: |
Gnus/5.130005 (Ma Gnus v0.5) Emacs/24.3 (gnu/linux) |
Mark H Weaver <address@hidden> skribis:
> address@hidden (Ludovic Courtès) writes:
>
>> Mark H Weaver <address@hidden> skribis:
>>
>>> It only makes sense to use 'par-map' when the procedure is fairly
>>> expensive to compute.
>>
>> Indeed.
>>
>>> There is inevitably a lot of overhead in creating and joining the
>>> threads.
>>
>> We use a thread pool, so there’s no such cost.
>
> Sorry, I was using the term 'threads' not in the sense of OS-level
> threads, but in a more general sense. I should have been more clear.
>
> What I meant is that from the user's perspective, threads are being
> created and joined, and even if you build those using a pool of OS-level
> threads, this inevitably involves thread synchronization, which is very
> expensive on modern architectures. So I maintain that there _is_ such a
> cost, and it can't be avoided.
Ah yes, OK.
> The point I was really trying to make here, in the simplest possible
> terms, is that it will *never* make sense to replace all uses of 'map'
> with 'par-map' wherever it is safe to do so.
Indeed!
Ludo’.
- Whats' the proper senario of par-map? (Was Re: bug#13188: par-map causes VM stack overflow), Nala Ginrut, 2013/03/27
- Re: Whats' the proper senario of par-map? (Was Re: bug#13188: par-map causes VM stack overflow), Mark H Weaver, 2013/03/28
- Re: Whats' the proper senario of par-map? (Was Re: bug#13188: par-map causes VM stack overflow), Nala Ginrut, 2013/03/28
- Re: Whats' the proper senario of par-map? (Was Re: bug#13188: par-map causes VM stack overflow), Mark H Weaver, 2013/03/29
- Extremely high overhead of 'par-map', Mark H Weaver, 2013/03/29
- Re: Extremely high overhead of 'par-map', Noah Lavine, 2013/03/29
- Re: Extremely high overhead of 'par-map', Noah Lavine, 2013/03/29
- Re: Extremely high overhead of 'par-map', Mark H Weaver, 2013/03/29
- Re: Extremely high overhead of 'par-map', Ludovic Courtès, 2013/03/30
- Re: Whats' the proper senario of par-map? (Was Re: bug#13188: par-map causes VM stack overflow), Mark H Weaver, 2013/03/29
- Re: Whats' the proper senario of par-map? (Was Re: bug#13188: par-map causes VM stack overflow), Ludovic Courtès, 2013/03/29