ide-cs using 100% CPU

ide-cs using 100% CPU

[Hamie]

I have a thinkpad r50p, 1.6GHz CPU, 512MB memory running kernel 
2.6.7-mm4 (Also tried 2.6.7, 2.6.6, 2.6.4 and a few others).

When reading from CF card (using ide-cs) the system is really stodgy and 
consumes 100% CPU. Almost all of it waitIO according to top...

Now it's not the fact that I get lots of waitIO, but AFAIUI if a system 
uses truckloads of waitIO, that should just mean that the system is idle 
but there's some IO going on & a process is waiting for it to complete 
(e.g. the way AIX does it).

Other processes should still be able to get CPU without any problems, 
but my experience is that under Linux if waitio is due to reading the CF 
card, the system essentially stops... The mouse still moves (Under X), 
but... unwillingly... Jerking around all over the place...

Anyone know why this happens? Something busy waiting? (BUt that should 
show as system cpu right?) or something taking out really long locks?

Re: ide-cs using 100% CPU

[Russell King]

On Sun, Jul 18, 2004 at 10:30:16AM +0100, Hamie wrote:
> Anyone know why this happens? Something busy waiting? (BUt that should 
> show as system cpu right?) or something taking out really long locks?

It'll be because IDE is using PIO to access the CF card, which could
have long access times (so reading a block of sectors could take some
time _and_ use CPU.)  Obviously, PIO requires the use of the CPU, so
the CPU can't be handed off to some other task while this is occuring.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core

Re: ide-cs using 100% CPU

[Hamie]

Russell King wrote:

>On Sun, Jul 18, 2004 at 10:30:16AM +0100, Hamie wrote:
>  
>
>>Anyone know why this happens? Something busy waiting? (BUt that should 
>>show as system cpu right?) or something taking out really long locks?
>>    
>>
>
>It'll be because IDE is using PIO to access the CF card, which could
>have long access times (so reading a block of sectors could take some
>time _and_ use CPU.)  Obviously, PIO requires the use of the CPU, so
>the CPU can't be handed off to some other task while this is occuring.
>
>  
>
Well... I did consider that. And not to disbelieve you, since you know 
the kernel way better than I do, But decided I was being silly that a 
1.6GHz Pentium-M processor should use 100% CPU moving a couple of 
MB/second across a CF interface...

Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU doing 
the same job as quick, or even slightly faster...

And should it not use system CPU rather than user CPU?

TIA
 Hamish.

Re: ide-cs using 100% CPU

[Russell King]

On Fri, Aug 06, 2004 at 08:33:52PM +0100, Hamie wrote:
> Russell King wrote:
> 
> >On Sun, Jul 18, 2004 at 10:30:16AM +0100, Hamie wrote:
> >  
> >
> >>Anyone know why this happens? Something busy waiting? (BUt that should 
> >>show as system cpu right?) or something taking out really long locks?
> >>    
> >>
> >
> >It'll be because IDE is using PIO to access the CF card, which could
> >have long access times (so reading a block of sectors could take some
> >time _and_ use CPU.)  Obviously, PIO requires the use of the CPU, so
> >the CPU can't be handed off to some other task while this is occuring.
> >
> >  
> >
> Well... I did consider that. And not to disbelieve you, since you know 
> the kernel way better than I do, But decided I was being silly that a 
> 1.6GHz Pentium-M processor should use 100% CPU moving a couple of 
> MB/second across a CF interface...
> 
> Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU doing 
> the same job as quick, or even slightly faster...
> 
> And should it not use system CPU rather than user CPU?

Actually, if its being accounted for as waitIO, then we should be
running some other task...  However, I've just realised that we
don't appear to specifically account IO waits in the kernel, so
I'm not sure how userspace comes up with this magic number.

Sorry for the noise...

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core

Re: ide-cs using 100% CPU

[Hamie]

Russell King wrote:

>On Fri, Aug 06, 2004 at 08:33:52PM +0100, Hamie wrote:
>  
>
>>Russell King wrote:
>>
>>    
>>
>>>On Sun, Jul 18, 2004 at 10:30:16AM +0100, Hamie wrote:
>>> 
>>>
>>>      
>>>
>>>>Anyone know why this happens? Something busy waiting? (BUt that should 
>>>>show as system cpu right?) or something taking out really long locks?
>>>>   
>>>>
>>>>        
>>>>
>>>It'll be because IDE is using PIO to access the CF card, which could
>>>have long access times (so reading a block of sectors could take some
>>>time _and_ use CPU.)  Obviously, PIO requires the use of the CPU, so
>>>the CPU can't be handed off to some other task while this is occuring.
>>>
>>> 
>>>
>>>      
>>>
>>Well... I did consider that. And not to disbelieve you, since you know 
>>the kernel way better than I do, But decided I was being silly that a 
>>1.6GHz Pentium-M processor should use 100% CPU moving a couple of 
>>MB/second across a CF interface...
>>
>>Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU doing 
>>the same job as quick, or even slightly faster...
>>
>>And should it not use system CPU rather than user CPU?
>>    
>>
>
>Actually, if its being accounted for as waitIO, then we should be
>running some other task...  However, I've just realised that we
>don't appear to specifically account IO waits in the kernel, so
>I'm not sure how userspace comes up with this magic number.
>
>Sorry for the noise...
>
>  
>

Hey... Make all the noise you like. If I knew the internals a bit more 
nowadays, I'd find it determine why it looks like userCPU myself.

Why doesn't the kernel account for waitIO? Design decision? or just not 
yet implemented? Or not wanted (Not sure why it'd be the third  or first 
:). Bug?

H

Re: ide-cs using 100% CPU

[Alan Cox]

On Gwe, 2004-08-06 at 20:33, Hamie wrote:
> Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU doing 
> the same job as quick, or even slightly faster...

PCMCIA IDE is PIO only so it burns CPU. This is one case where
hyperthreading is nice. Cardbus IDE is a lot better but very little
exists and we don't currently support hotplug IDE controllers.

> And should it not use system CPU rather than user CPU?

Yes - but figure out please if the kernel or userspace is getting that
wrong ;)

Alan

Re: ide-cs using 100% CPU

[Hamie]

Alan Cox wrote:

>On Gwe, 2004-08-06 at 20:33, Hamie wrote:
>  
>
>>Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU doing 
>>the same job as quick, or even slightly faster...
>>    
>>
>
>PCMCIA IDE is PIO only so it burns CPU. This is one case where
>hyperthreading is nice. Cardbus IDE is a lot better but very little
>exists and we don't currently support hotplug IDE controllers.
>
>  
>

Ah right. But would a CF memory card be cardbus anyway?

>>And should it not use system CPU rather than user CPU?
>>    
>>
>
>Yes - but figure out please if the kernel or userspace is getting that
>wrong ;)
>
>  
>

My apologies. It was gkrellm leading me up the garden path on that 
one... Copying about 100MB from a 512MB CF card (25+ photos from my 
camera) vmstat 5 reports 4% usercpu, 96% system cpu. And the response on 
the system is sluggish to say the least. (Moving the pointer in X is 
painful :). gkrell meanwhile on it's cpu graph shows about 30% system, 
and the rest as userCPU. No idea why, I guess till I find out I'll just 
regard gkrellm's cpu graph as a waste of space (To differentiate system 
& user cpu anyway :).


>  
>

Re: ide-cs using 100% CPU

[Alan Cox]

hdparm -u1 /dev/hd[whatever]

will help a lot on the sluggishness

Re: ide-cs using 100% CPU

[Paulo Marques]

Hamie wrote:
> Alan Cox wrote:
> 
>> On Gwe, 2004-08-06 at 20:33, Hamie wrote:
>>  
>>
>>> Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU 
>>> doing the same job as quick, or even slightly faster...
>>>   
>>
>>
>> PCMCIA IDE is PIO only so it burns CPU. This is one case where
>> hyperthreading is nice. Cardbus IDE is a lot better but very little
>> exists and we don't currently support hotplug IDE controllers.
>>
>>  
>>
> 
> Ah right. But would a CF memory card be cardbus anyway?

I've never seen a CF card that supported DMA (and I've worked with 
several brands). Compact Flash cards have several modes of operation and 
only one of this modes is "IDE-compatible".

> 
>>> And should it not use system CPU rather than user CPU?
>>>   
>>
>>
>> Yes - but figure out please if the kernel or userspace is getting that
>> wrong ;)
>>
>>  
>>
> 
> My apologies. It was gkrellm leading me up the garden path on that 
> one... Copying about 100MB from a 512MB CF card (25+ photos from my 
> camera) vmstat 5 reports 4% usercpu, 96% system cpu. And the response on 
> the system is sluggish to say the least. (Moving the pointer in X is 
> painful :). gkrell meanwhile on it's cpu graph shows about 30% system, 
> and the rest as userCPU. No idea why, I guess till I find out I'll just 
> regard gkrellm's cpu graph as a waste of space (To differentiate system 
> & user cpu anyway :).

I think this is more of a scheduler/priorities problem. Maybe all the 
work that is being done with staircase / low-latency will help you on 
this :)

-- 
Paulo Marques - www.grupopie.com
"In a world without walls and fences who needs windows and gates?"

Re: ide-cs using 100% CPU

[P]

Paulo Marques wrote:
> I've never seen a CF card that supported DMA (and I've worked with 
> several brands). Compact Flash cards have several modes of operation and 
> only one of this modes is "IDE-compatible".

The newer ones do. I've a SanDisk SDCFB-64-201-80 that
hangs on boot because it reports that it supports DMA
but the ide adapter I use does not connect the DMA request
and grant signals. A work around is to boot with ide=nodma
however this is system wide.

Pádraig.

Re: ide-cs using 100% CPU

[Bill Davidsen]

Alan Cox wrote:
> On Gwe, 2004-08-06 at 20:33, Hamie wrote:
> 
>>Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU doing 
>>the same job as quick, or even slightly faster...
> 
> 
> PCMCIA IDE is PIO only so it burns CPU. This is one case where
> hyperthreading is nice. Cardbus IDE is a lot better but very little
> exists and we don't currently support hotplug IDE controllers.
> 
> 
>>And should it not use system CPU rather than user CPU?
> 
> 
> Yes - but figure out please if the kernel or userspace is getting that
> wrong ;)

He didn't mention seeing waitio in his stats (or I missed it) so he may 
be using old userspace tools which don't show waitio.

Should this show as system or waitio? Typically waitio time can be used 
for other thaings and this can't, so perhaps showing it as system is 
correct in this case.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me

Re: ide-cs using 100% CPU

[Robert Hancock]

It isn't that the CPU is doing so much work, it's mostly waiting. However
with this type of PIO access, the CPU must do all the reads/writes from the
buffer and while doing this the CPU is blocked and cannot do anything else.


----- Original Message ----- 
From: "Hamie" <hamish@travellingkiwi.com>
Newsgroups: fa.linux.kernel
To: "Russell King" <rmk+lkml@arm.linux.org.uk>
Cc: <linux-kernel@vger.kernel.org>
Sent: Friday, August 06, 2004 1:46 PM
Subject: Re: ide-cs using 100% CPU


> Russell King wrote:
>
> >On Sun, Jul 18, 2004 at 10:30:16AM +0100, Hamie wrote:
> >
> >
> >>Anyone know why this happens? Something busy waiting? (BUt that should
> >>show as system cpu right?) or something taking out really long locks?
> >>
> >>
> >
> >It'll be because IDE is using PIO to access the CF card, which could
> >have long access times (so reading a block of sectors could take some
> >time _and_ use CPU.)  Obviously, PIO requires the use of the CPU, so
> >the CPU can't be handed off to some other task while this is occuring.
> >
> >
> >
> Well... I did consider that. And not to disbelieve you, since you know
> the kernel way better than I do, But decided I was being silly that a
> 1.6GHz Pentium-M processor should use 100% CPU moving a couple of
> MB/second across a CF interface...
>
> Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU doing
> the same job as quick, or even slightly faster...
>
> And should it not use system CPU rather than user CPU?
>
> TIA
>  Hamish.
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> More majordomo info at  http://vger.kernel.org/majordomo-info.html
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Re: ide-cs using 100% CPU

[Hamie]

Robert Hancock wrote:

>It isn't that the CPU is doing so much work, it's mostly waiting. However
>  
>

That was my point... While waiting, shouldn't the CPU be off doing 
something else? Like giving X some attention...

>with this type of PIO access, the CPU must do all the reads/writes from the
>buffer and while doing this the CPU is blocked and cannot do anything else.
>
>  
>

Or is the CF requirements such that it's spending it's time doing the 
actual reads & writes from the buffer, and it's the hardware inserting 
wait-states when it's being accessed?

Re: ide-cs using 100% CPU

[Robert Hancock]

----- Original Message ----- 
From: "Hamie" <hamish@travellingkiwi.com>


> Robert Hancock wrote:
>
> >It isn't that the CPU is doing so much work, it's mostly waiting. However
> >
> >
>
> That was my point... While waiting, shouldn't the CPU be off doing
> something else? Like giving X some attention...
>
> >with this type of PIO access, the CPU must do all the reads/writes from
the
> >buffer and while doing this the CPU is blocked and cannot do anything
else.
> >
> >
> >
>
> Or is the CF requirements such that it's spending it's time doing the
> actual reads & writes from the buffer, and it's the hardware inserting
> wait-states when it's being accessed?
>

That's basically what's happening, when the CPU does a write or a read of
some data from the buffer, it has to wait for that to go all the way across
the bus and to/from the card, meanwhile no other useful work can be done
while it is waiting. As Alan Cox mentioned, having a hyperthreaded CPU helps
tremendously in such cases, since the other "half" of the CPU can be doing
useful work while the first half is blocked.