More ULE bugs fixed.
Jeff Roberson
jroberson at chesapeake.net
Thu Oct 16 23:28:26 PDT 2003
On Fri, 17 Oct 2003, Bruce Evans wrote:
> How would one test if it was an improvement on the 4BSD scheduler? It
> is not even competitive in my simple tests.
[scripts results deleted]
>
> Summary: SCHED_ULE was more than twice as slow as SCHED_4BSD for the
> obj and depend stages. These stages have little parallelism. SCHED_ULE
> was only 19% slower for the all stage. It apparently misses many
> oppurtunities to actually run useful processes. This may be related
> to /usr being nfs mounted. There is lots of idling waiting for nfs
> even in the SCHED_4BSD case. The system times are smaller for SCHED_ULE,
> but this might not be significant. E.g., zeroing pages can account
> for several percent of the system time in buildworld, but on unbalanced
> systems that have too much idle time most page zero gets done in idle
> time and doesn't show up in the system time.
At one point ULE was at least as fast as 4BSD and in most cases faster.
This is a regression. I'll sort it out soon.
>
> Test 1 for fair scheduling related to niceness:
>
> for i in 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
> do
> nice -$i sh -c "while :; do echo -n;done" &
> done
> top -o time
>
> [Output deleted]. This shows only a vague correlation between niceness
> and runtime for SCHED_ULE. However, top -o cpu shows a strong correlation
> between %CPU and niceness. Apparently, %CPU is very innacurate and/or
> not enough history is kept for long-term scheduling to be fair.
>
> Test 5 for fair scheduling related to niceness:
>
> for i in -20 -16 -12 -8 -4 0 4 8 12 16 20
> do
> nice -$i sh -c "while :; do echo -n;done" &
> done
> time top -o cpu
>
> With SCHED_ULE, this now hangs the system, but it worked yesterday. Today
> it doesn't get as far as running top and it stops the nfs server responding.
> To unhang the system and see what the above does, run a shell at rtprio 0
> and start top before the above, and use top to kill processes (I normally
> use "killall sh" to kill all the shells generated by tests 1-5, but killall
> doesn't work if it is on nfs when the nfs server is not responding).
661 root 112 -20 900K 608K RUN 0:24 27.80% 27.64% sh
662 root 114 -16 900K 608K RUN 0:19 12.43% 12.35% sh
663 root 114 -12 900K 608K RUN 0:15 10.66% 10.60% sh
664 root 114 -8 900K 608K RUN 0:11 9.38% 9.33% sh
665 root 115 -4 900K 608K RUN 0:10 7.91% 7.86% sh
666 root 115 0 900K 608K RUN 0:07 6.83% 6.79% sh
667 root 115 4 900K 608K RUN 0:06 5.01% 4.98% sh
668 root 115 8 900K 608K RUN 0:04 3.83% 3.81% sh
669 root 115 12 900K 608K RUN 0:02 2.21% 2.20% sh
670 root 115 16 900K 608K RUN 0:01 0.93% 0.93% sh
I think you cvsup'd at a bad time. I fixed a bug that would have caused
the system to lock up in this case late last night. On my system it
freezes for a few seconds and then returns. I can stop that by turning
down the interactivity threshold.
Thanks,
Jeff
>
> Bruce
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