2.5.47 scheduler problems?

2.5.47 scheduler problems?

Post by Mike Galbrait » Tue, 19 Nov 2002 08:30:08



Greetings,

For testing swap throughput, I like to run make -j30 bzImage on my 500Mhz
PIII w. 128Mb ram.  For testing interactivity, I fire up KDE, start a
smaller make -j, grab a window, and wave it around.

With 2.4.20rc2+rc1aa1, running a -j10 build (not swapping) is very very
bad.  However, if I set all tasks in the system to SCHED_FIFO or SCHED_RR
prior to this light make -j, I have a ~pretty smooth system.

If I do the same in 2.5.47, I have no control of my box.  Setting all tasks
to SCHED_FIFO or SCHED_RR prior to starting make -j10 bzImage, I can regain
control, but interactivity under load is basically not present.

I used to be able to wave a window poorly at make -j25 (swapping heftily),
fairly smoothly at make -j20, and smoothly at make -j15 or below.  This
with no SCHED_RR/SCHED_FIFO.  (I haven't done much testing like this in
quite a while though)

        -Mike

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2.5.47 scheduler problems?

Post by Tim Connor » Tue, 19 Nov 2002 09:00:08



> Greetings,

> For testing swap throughput, I like to run make -j30 bzImage on my 500Mhz
> PIII w. 128Mb ram.  For testing interactivity, I fire up KDE, start a
> smaller make -j, grab a window, and wave it around.

> With 2.4.20rc2+rc1aa1, running a -j10 build (not swapping) is very very
> bad.  However, if I set all tasks in the system to SCHED_FIFO or SCHED_RR
> prior to this light make -j, I have a ~pretty smooth system.

> If I do the same in 2.5.47, I have no control of my box.  Setting all tasks
> to SCHED_FIFO or SCHED_RR prior to starting make -j10 bzImage, I can regain
> control, but interactivity under load is basically not present.

Funny that.

Quote:> I used to be able to wave a window poorly at make -j25 (swapping heftily),
> fairly smoothly at make -j20, and smoothly at make -j15 or below.  This
> with no SCHED_RR/SCHED_FIFO.  (I haven't done much testing like this in
> quite a while though)

Perhaps you should consider buying an extra 29 CPU's for you desktop?

--
TimC -- http://astronomy.swin.edu.au/staff/tconnors/

A Chemist who falls in acid is absorbed in work.

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2.5.47 scheduler problems?

Post by Andrew Morto » Tue, 19 Nov 2002 09:10:07



> > I used to be able to wave a window poorly at make -j25 (swapping heftily),
> > fairly smoothly at make -j20, and smoothly at make -j15 or below.  This
> > with no SCHED_RR/SCHED_FIFO.  (I haven't done much testing like this in
> > quite a while though)

> Perhaps you should consider buying an extra 29 CPU's for you desktop?

No.  He's saying that it used to be OK, but it has got worse.

A much simpler test is to start a big compilation and then madly
waggle an X window around.  Goes OK for a few seconds, and then
seizes up quite horridly.  Presumably because the scheduler has
suddenly decided that the X server has become a "batch" process
and is scheduling it in a similar manner to the compilation.

If you stop wiggling the window for 5-10 seconds it comes back.
Presumably because the scheduler has decided that the X server is
"interactive" again.

When it happens, it's *very* bad.  The mouse cursor doesn't move
for 0.5-1.0 seconds and then takes great leaps.  It is unusable.

Strangely it does not happen (much) when the background load is
a few busywaits.  It has to be a compilation - maybe short-lived
batch processes is what triggers it.

For me, the X server is sometimes the victim, and the MUA (netscape4)
is frequently victimised.  This is because the MUA alternates between
periods of interactivity and periods of compute-intensive work (parsing
large mailboxes).   When this problem strikes you have to just sit there
with your arms folded waiting for it to stop.

It needs fixing.
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2.5.47 scheduler problems?

Post by Mike Galbrait » Tue, 19 Nov 2002 09:40:05


----- Original Message -----


Sent: Monday, November 18, 2002 7:51 AM
Subject: Re: 2.5.47 scheduler problems?


> > Greetings,

> > For testing swap throughput, I like to run make -j30 bzImage on my
500Mhz
> > PIII w. 128Mb ram.  For testing interactivity, I fire up KDE, start
a
> > smaller make -j, grab a window, and wave it around.

> > With 2.4.20rc2+rc1aa1, running a -j10 build (not swapping) is very
very
> > bad.  However, if I set all tasks in the system to SCHED_FIFO or
SCHED_RR
> > prior to this light make -j, I have a ~pretty smooth system.

> > If I do the same in 2.5.47, I have no control of my box.  Setting
all tasks
> > to SCHED_FIFO or SCHED_RR prior to starting make -j10 bzImage, I can
regain
> > control, but interactivity under load is basically not present.

> Funny that.

> > I used to be able to wave a window poorly at make -j25 (swapping
heftily),
> > fairly smoothly at make -j20, and smoothly at make -j15 or below.
This
> > with no SCHED_RR/SCHED_FIFO.  (I haven't done much testing like this
in
> > quite a while though)

> Perhaps you should consider buying an extra 29 CPU's for you desktop?

I have neither the need for 30 CPUs, nor the cash to pay for such a
beast :)

I gather you think my test is silly?

    -Mike

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2.5.47 scheduler problems?

Post by Mike Galbrait » Tue, 19 Nov 2002 09:50:05


----- Original Message -----



Sent: Monday, November 18, 2002 8:08 AM
Subject: Re: 2.5.47 scheduler problems?


> > > I used to be able to wave a window poorly at make -j25 (swapping
heftily),
> > > fairly smoothly at make -j20, and smoothly at make -j15 or below.
This
> > > with no SCHED_RR/SCHED_FIFO.  (I haven't done much testing like
this in
> > > quite a while though)

> > Perhaps you should consider buying an extra 29 CPU's for you
desktop?

> No.  He's saying that it used to be OK, but it has got worse.

> A much simpler test is to start a big compilation and then madly
> waggle an X window around.  Goes OK for a few seconds, and then
> seizes up quite horridly.  Presumably because the scheduler has
> suddenly decided that the X server has become a "batch" process
> and is scheduling it in a similar manner to the compilation.

> If you stop wiggling the window for 5-10 seconds it comes back.
> Presumably because the scheduler has decided that the X server is
> "interactive" again.

> When it happens, it's *very* bad.  The mouse cursor doesn't move
> for 0.5-1.0 seconds and then takes great leaps.  It is unusable.

I was watching it this morning, without wiggling, and it seems to update
window content (make output in one and vmstat in another) about every 5
seconds.. very odd looking.

    -Mike

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2.5.47 scheduler problems?

Post by Tim Connor » Tue, 19 Nov 2002 10:00:11



> > > If I do the same in 2.5.47, I have no control of my box.  Setting
> all tasks
> > > to SCHED_FIFO or SCHED_RR prior to starting make -j10 bzImage, I can
> regain
> > > control, but interactivity under load is basically not present.

> > Funny that.

> > > I used to be able to wave a window poorly at make -j25 (swapping
> heftily),
> > > fairly smoothly at make -j20, and smoothly at make -j15 or below.
> This
> > > with no SCHED_RR/SCHED_FIFO.  (I haven't done much testing like this
> in
> > > quite a while though)

> > Perhaps you should consider buying an extra 29 CPU's for you desktop?

> I have neither the need for 30 CPUs, nor the cash to pay for such a
> beast :)

> I gather you think my test is silly?

Well, yes, 30 processes at a time on a single CPU does seem a bit silly -
given that (under the old system), you would not expect X to get more than
3% of the CPU time.
Also sceduling normal processes (ie, not real-time processes) as RR/FIFO
seemed also pretty bad.

However....

But I have to now admit that I haven't yet played with 2.5.47 seriously,
and wansn't aware of the problems which Andrew just posted.

mea culpa.

--
TimC -- http://astronomy.swin.edu.au/staff/tconnors/

If you ever fear that machines will surpass humans in intelligence,
just ask Microsoft to write the OS.     -- POTU in RHOD

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2.5.47 scheduler problems?

Post by Mike Galbrait » Tue, 19 Nov 2002 13:10:07


----- Original Message -----



Sent: Monday, November 18, 2002 8:53 AM
Subject: Re: 2.5.47 scheduler problems?


> > > > If I do the same in 2.5.47, I have no control of my box.
Setting
> > all tasks
> > > > to SCHED_FIFO or SCHED_RR prior to starting make -j10 bzImage, I
can
> > regain
> > > > control, but interactivity under load is basically not present.

> > > Funny that.

> > > > I used to be able to wave a window poorly at make -j25 (swapping
> > heftily),
> > > > fairly smoothly at make -j20, and smoothly at make -j15 or
below.
> > This
> > > > with no SCHED_RR/SCHED_FIFO.  (I haven't done much testing like
this
> > in
> > > > quite a while though)

> > > Perhaps you should consider buying an extra 29 CPU's for you
desktop?

> > I have neither the need for 30 CPUs, nor the cash to pay for such a
> > beast :)

> > I gather you think my test is silly?

> Well, yes, 30 processes at a time on a single CPU does seem a bit
silly -
> given that (under the old system), you would not expect X to get more
than
> 3% of the CPU time.

I don't try -j30 with X/KDE running.. that's much too heavy for my
little box.  The whole point of doing -j30 on my box without X/KDE is
that it juuuust fills up capacity.  It generally adds a minute to build
time despite quite hefty swapping.  With aa kernels or heavily twiddled
stock kernels, it's more like 30 seconds.  (with new gcc, -j30 is way
too much too.. oink oink;)

> Also sceduling normal processes (ie, not real-time processes) as
RR/FIFO
> seemed also pretty bad.

That was only to see if I _could_ get some CPU, and with (only:) 10
copies of gcc running.

> However....

> But I have to now admit that I haven't yet played with 2.5.47
seriously,
> and wansn't aware of the problems which Andrew just posted.

> mea culpa.

> --
> TimC -- http://astronomy.swin.edu.au/staff/tconnors/

    -Mike

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1. 2.5.47 scheduler problems?

Hi Mike, Rik, Everyone,

The O(1) schedule just isn't fair.  It will run a subset
of the runable processes excluding the rest.  See my earlier
emails for the details.

I had been working on a fix for this but got distracted
by Posix timers.  I still hope to get back to it.

My patch is here:
http://marc.theaimsgroup.com/?l=linux-kernel&m=103508412423719&w=2

It fixes fairness but breaks nice(2). Rik van Riel has a
patch here which builds on my patch which fixes this:
http://marc.theaimsgroup.com/?l=linux-kernel&m=103651801424031&w=2

I just gave this a spin with.  The patches still apply cleanly
to linux-2.5.48 and it seems well behaved:-)  

I found this problem with the LTP waitpid06 test.  It actually
produced a live-lock. See this mail:
http://marc.theaimsgroup.com/?l=linux-kernel&m=103133744217082&w=2

Jim Houston - Concurrent Computer Corp.
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