Re: [patch] "HT scheduler", sched-2.5.63-B3

[Mike Galbraith <efault@gmx.de>]

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At 12:42 PM 3/6/2003 -0800, Andrew Morton wrote:
>Ingo's combo patch is better still - that is sched-2.5.64-a5 and your patch
>combined (yes?).  The slight mouse jerkiness is gone and even when doing
>really silly things I cannot make it misbehave at all.  I'd handwavingly
>describe both your patch and sched-2.5.64-a5 as 80% solutions, and the combo
>95%.

Weeeeell, FWIW my box (p3-500/128mb/rage128) disagrees.

I can still barely control the box when a make -j5 bzImage is running under 
X/KDE in one terminal and a vmstat (SCHED_RR) in another. I'm not swapping, 
though a bit of idle junk does page out.  IOW, I think I'm seeing serious 
cpu starvation.

For reference, I used to be able to easily control the same box under X 
while swapping moderately at make -j15 (during page aging vm days), and 
with a heavily twiddled VM at even -j30 (_way_ overloaded with X oinkers 
running).  At -j5, gui/icky was quite usable.

With the make -j30 bzImage, heavy load which does _hit_ VM saturation but 
not constantly, I see what I can only describe as starvation.  vmstat 
output for this load is definitely abby-normal, and there's no way 
/proc/vmstat should look like the attached.  It takes forever to build 
enough vm pressure that swap is touched (bad bad bad), and the volume 
reached is way low.  My hungry little cc1's are not sharing resources the 
way they should be (methinks).

With earlier versions of Ingo's patch, I was only able to get memory 
pressure up to where it should be by drastically reducing timeslice (at the 
expense of turning throughput to crud).  Take this with a giant economy 
sized grain of salt, but what I _think_ (no, I haven't instrumented it) is 
happening is that chunks of the total job are being rescheduled in front of 
the rest of the job such that they alloc/use/exit before the other guys can 
alloc.  (geez that's a nebulous WAG;)

         -Mike  (please torch me if I'm being stupid;) 

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box = p3/500/128MB
fresh boot
time make -j30 bzImage
cat /proc/vmstat

                  2.5.64-B3  2.5.64-virgin
------------------------------------------
nr_dirty                 64           2448
nr_writeback              0              0
nr_pagecache           7432           7562
nr_page_table_pages      85             85
nr_reverse_maps        3348           3177
nr_mapped               634            579
nr_slab                1239           1235
pgpgin               288560         692725
pgpgout              228803         587572
pswpin                30734         116097
pswpout               47347         138888
pgalloc              918016        1046369
pgfree               940744        1068983
pgactivate            28577          45566
pgdeactivate          55265         172833
pgfault             1579517        1682466
pgmajfault             8463          28137
pgscan               556041        1678315
pgrefill             211542         643564
pgsteal               77311         194216
pginodesteal              0              0
kswapd_steal          73454         173378
kswapd_inodesteal     11069          11317
pageoutrun              222            509
allocstall               85            480
pgrotated             49798         140956