From: Paul Rubin <no.email@nospam.invalid>
Subject: Re: Large number of tasks slows down my program (using debian) - any fix?
Date: Fri, 30 Mar 2018 13:46:10 -0700
Date: 2018-03-30T13:46:10-07:00 [thread overview]
Message-ID: <87h8ox1ect.fsf@nightsong.com> (raw)
In-Reply-To: p9kuig$lq8$1@gioia.aioe.org
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> It is a simple calculation. Assuming a context switch were around
> 1000ns. x 500 tasks / 4 cores = 125ms if all tasks are busy. 125ms is
> a long time.
It's 125 microseconds or 1/8th of a millisecond, not that bad at all. I
assume that's what you meant by ms. I'm used to ms denoting
milliseconds while microseconds are written us.
Also keep in mind that 4-core Intel boxes typically have 8 hardware
threads ("hyperthreads" or logical cores) and there is basically no
context switch time between hyperthreads on a core. They speed up total
cpu throughput because they allow another thread to run during the time
that the first thread is blocked on a hardware cache miss waiting for a
RAM operation.
> ... Assuming the time quant is 10ms...: 10 x 500 / 4 = 1.25s [+125ms]
> is the time a task gets back to a core. 1.3s is an eternity.
Sure, if all 500 tasks are cpu-busy then things are in a dreadful state,
but usually the reason to use so many tasks is concurrent i/o, i.e. most
of the threads are blocked awaiting input.
next prev parent reply other threads:[~2018-03-30 20:46 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-28 18:06 Large number of tasks slows down my program (using debian) - any fix? reinert
2018-03-28 18:49 ` Dennis Lee Bieber
2018-03-28 19:06 ` Paul Rubin
2018-03-28 19:21 ` Dmitry A. Kazakov
2018-03-28 20:17 ` reinert
2018-03-29 8:46 ` reinert
2018-03-29 9:18 ` Dmitry A. Kazakov
2018-03-29 15:39 ` Jeffrey R. Carter
2018-04-15 5:20 ` reinert
2018-03-29 22:33 ` Shark8
2018-03-30 9:04 ` Dmitry A. Kazakov
2018-03-30 20:46 ` Paul Rubin [this message]
2018-03-31 0:09 ` Randy Brukardt
2018-03-31 6:00 ` Paul Rubin
2018-03-31 9:37 ` Jacob Sparre Andersen
2018-03-31 10:44 ` Dmitry A. Kazakov
2018-04-02 3:35 ` Randy Brukardt
2018-04-02 6:23 ` alby.gamper
2018-04-02 7:12 ` alby.gamper
2018-04-05 14:07 ` Brad Moore
2018-04-05 15:09 ` Dmitry A. Kazakov
2018-04-07 4:16 ` Brad Moore
2018-04-05 15:30 ` Jeffrey R. Carter
2018-04-05 19:33 ` Spiros Bousbouras
2018-04-05 19:44 ` Simon Wright
2018-04-05 20:25 ` Jeffrey R. Carter
2018-04-06 5:58 ` Benchmarks Game: Thread ring (Was: Large number of tasks slows down my program (using debian) - any fix?) Jacob Sparre Andersen
2018-04-07 4:28 ` Brad Moore
2018-04-06 15:48 ` Large number of tasks slows down my program (using debian) - any fix? Jeffrey R. Carter
2018-04-07 4:39 ` Brad Moore
2018-04-07 8:15 ` Jeffrey R. Carter
2018-04-07 16:28 ` Brad Moore
2018-04-07 18:41 ` Jeffrey R. Carter
2018-04-08 0:29 ` Brad Moore
2018-04-08 8:25 ` Jeffrey R. Carter
2018-04-08 0:06 ` Robert I. Eachus
2018-04-07 16:51 ` Brad Moore
2018-04-07 12:21 ` Simon Wright
2018-04-07 16:57 ` Brad Moore
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