ULE 2.0

[Jeff Roberson]

Some last minute inspiration has the nice response looking much more 
favorable.  This will be the last of my changes until I have some 
feedback.

Thanks,
Jeff

On Thu, 4 Jan 2007, Jeff Roberson wrote:

> Hello everyone,
>
> After a considerable vacation from ULE I have come back to address some long 
> standing concerns.  I felt that the old double-queue mechanism caused very 
> unnatural behavior and have finally come up with something I'm happy to 
> replace it with.  I've been working on this off and on for several months 
> now.  Some details are below.  More are at:
> http://jeffr-tech.livejournal.com/3729.html
>
> The version now in CVS(1.172) should restore ULE's earlier interactive 
> performance under load.  I have tested with a make -j128 kernel while using 
> mozilla and while playing a dvd.  Neither ever skip for me.  nice now has a 
> more gradual effect than before.  It no longer allows the total starvation of 
> processes.  ULE should also be very slightly faster on UP as compared to 
> before.  SMP behavior should have changed very little although I did simplify 
> some small parts of these algorithms.  In general, non-interactive tasks are 
> scheduled much more intelligently although this may not be apparent under 
> most workloads.
>
> I'm hoping for the following types of feedback from anyone interested in 
> testing:
>
> 1)  Is the response to nice levels as you would hope?  I think nice +20 may 
> not inhibit the nice'd thread enough at the moment.
> 2)  Is the interactive performance satisfactory?
> 3)  Is there any performance degredation for your common tasks?
> 4)  Does the cpu estimator give reasonable results?  See %cpu in top.  It is 
> expected that there will be periods where summing up all threads will yield 
> slightly over 100% cpu.
>
> Any and all feedback is welcome.  Please make sure any problem reports are 
> sent to jroberson at chesapeake.net in the to line so I see them more quickly.
>
> Thanks,
> Jeff
>
> ---------- Forwarded message ----------
> Date: Thu, 4 Jan 2007 08:56:25 +0000 (UTC)
> From: Jeff Roberson <jeff at FreeBSD.org>
> To: src-committers at FreeBSD.org, cvs-src at FreeBSD.org, cvs-all at FreeBSD.org
> Subject: cvs commit: src/sys/kern sched_ule.c
>
> jeff        2007-01-04 08:56:25 UTC
>
>  FreeBSD src repository
>
>  Modified files:
>    sys/kern             sched_ule.c
>  Log:
>  ULE 2.0:
>   - Remove the double queue mechanism for timeshare threads.  It was slow
>     due to excess cache lines in play, caused suboptimal scheduling behavior
>     with niced and other non-interactive processes, complicated priority
>     lending, etc.
>   - Use a circular queue with a floating starting index for timeshare 
> threads.
>     Enforces fairness by moving the insertion point closer to threads with
>     worse priorities over time.
>   - Give interactive timeshare threads real-time user-space priorities and
>     place them on the realtime/ithd queue.
>   - Select non-interactive timeshare thread priorities based on their cpu
>     utilization over the last 10 seconds combined with the nice value.  This
>     gives us more sane priorities and behavior in a loaded system as
>     compared to the old method of using the interactivity score.  The
>     interactive score quickly hit a ceiling if threads were non-interactive
>     and penalized new hog threads.
>   - Use one slice size for all threads.  The slice is not currently
>     dynamically set to adjust scheduling behavior of different threads.
>   - Add some new sysctls for scheduling parameters.
>
>  Bug fixes/Clean up:
>   - Fix zeroing of td_sched after initialization in sched_fork_thread() 
> caused
>     by recent ksegrp removal.
>   - Fix KSE interactivity issues related to frequent forking and exiting of
>     kse threads.  We simply disable the penalty for thread creation and exit
>     for kse threads.
>   - Cleanup the cpu estimator by using tickincr here as well.  Keep ticks 
> and
>     ltick/ftick in the same frequency.  Previously ticks were stathz and
>     others were hz.
>   - Lots of new and updated comments.
>   - Many many others.
>
>  Tested on:      up x86/amd64, 8way amd64.
>
>  Revision  Changes    Path
>  1.172     +332 -412  src/sys/kern/sched_ule.c
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