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From: Bill Davidsen <davidsen@tmr.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Arjan van de Ven <arjan@infradead.org>, linux-kernel@vger.kernel.org
Subject: Re: [ANN] Userspace M-on-N threading model implementation. Alpha release.
Date: Sun, 04 Feb 2007 16:42:43 -0500	[thread overview]
Message-ID: <45C65353.5000602@tmr.com> (raw)
In-Reply-To: <20070204202053.GC20307@devserv.devel.redhat.com>

Jakub Jelinek wrote:
> On Sun, Feb 04, 2007 at 03:12:32PM -0500, Bill Davidsen wrote:
>   
>> Arjan van de Ven wrote:
>>     
>>>> Because user threading can avoid context switches, there will always be 
>>>> cases where it will outperform o/s threads for hardware reasons.
>>>>         
>>> actually.. switching from one "real" thread to another in Linux is not
>>> an actual context switch in the hardware sense... at least this part of
>>> your argument seems to be incorrect ;)
>>>
>>>       
>> How does that work? Switching between kernel threads requires going into 
>> the kernel, user level thread switches are all done in user mode.
>>
>> Do you have some way to change o/s threads w/o going into the kernel?
>>     
>
> But going into kernel is not very expensive on Linux.
>
> On the other side, the overhead you need to add for every single syscall
> that might block for the M:N threads and the associated complications
> which make it far harder to conform to POSIX IMHO far outweight the costs
> of going into the kernel for a context switch.

That really wasn't my question, Arjan said that switching real threads 
wasn't a context switch in the hardware sense, and I was asking if I 
missed something. It may be cheap, but it would seem to be a context 
switch none-the-less.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979


  reply	other threads:[~2007-02-04 21:42 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-30 21:16 Kaz Kylheku
2007-01-31  8:47 ` Evgeniy Polyakov
2007-02-02 16:12 ` Bill Davidsen
2007-02-03 15:26   ` Arjan van de Ven
2007-02-04 20:12     ` Bill Davidsen
2007-02-04 20:20       ` Jakub Jelinek
2007-02-04 21:42         ` Bill Davidsen [this message]
2007-02-05  6:14           ` Arjan van de Ven
2007-02-14 12:17           ` Pavel Machek
2007-02-04 22:52         ` Davide Libenzi
  -- strict thread matches above, loose matches on Subject: below --
2007-01-29 14:52 Evgeniy Polyakov
2007-01-29 14:57 ` Evgeniy Polyakov
2007-01-29 16:40 ` Chris Friesen
2007-01-30  9:46   ` Evgeniy Polyakov
     [not found] ` <40f323d00701290747y68c8e27ege824694bfa378f58@mail.gmail.com>
2007-01-30  1:18   ` Samuel Thibault
2007-01-30  9:53     ` Evgeniy Polyakov
2007-01-30 10:24       ` Samuel Thibault
2007-01-30 10:43         ` Evgeniy Polyakov
2007-02-01  4:28 ` Lee Revell
2007-02-01  7:09   ` Evgeniy Polyakov

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