Messages in this thread | | | Date | Sun, 04 Feb 2007 16:42:43 -0500 | From | Bill Davidsen <> | Subject | Re: [ANN] Userspace M-on-N threading model implementation. Alpha release. |
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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
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