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SubjectRe: PROMBLEM: CD burning at 16x uses excessive CPU, although DMA is enabled
Date
Hi,

I tested with my computer - the CD-R:s that I had
limited the testing to 10x. But when testing
that it indicated 33% CPU in system, but not accouted
to any process by top.

I have done some profiling with my kernel
2.4.17-rmap12f
I think this indicates that the time spent for this kernel is
IRQ happening during idle time - correct?

I am not sure that this is the same situation that Anssi has
but 33% are quite a lot (more than he got, DMAs are enabled).
But at least it is another comparative datapoint...

/RogerL

--- output from readprofile (>=3) ------------------
3 __aux_write_ack 0.0938
3 kmalloc 0.0115
3 pipe_poll 0.0300
3 sys_select 0.0026
4 add_wait_queue 0.1000
4 link_path_walk 0.0021
4 rest_init 0.1000
4 rmqueue 0.0059
4 tasklet_action 0.0303
4 timer_bh 0.0066
5 __free_pages_ok 0.0068
5 sock_poll 0.1250
6 __rdtsc_delay 0.2143
6 __switch_to 0.0326
6 __wake_up 0.0375
6 kfree 0.0405
7 fget 0.1750
7 poll_freewait 0.1029
7 sys_write 0.0357
8 unix_poll 0.0541
9 schedule 0.0110
11 do_softirq 0.0671
12 do_anonymous_page 0.0517
12 do_select 0.0252
23 handle_IRQ_event 0.2614
24 file_read_actor 0.1765
5960 ide_intr 17.7381
36056 default_idle 901.4000
42283 total 0.0418

On måndagen den 8 april 2002 21.06, Anssi Saari wrote:
> On Mon, Apr 08, 2002 at 01:35:35PM -0400, Bill Davidsen wrote:
> > Okay, this is good information. At the risk of asking a dumb question,
> > are you sure that both the burner and the source drive ar using DMA?
>
> I'm fairly certain. I can read that test image at ~37MB/s and 35% CPU,
> which can't be PIO. The CD writer reads at ~3.7MB/s and 3% CPU usage.
>
> > that they are on separate cables (controllers)?
>
> Yes. Two HDs, one writer, all on different channels. The other HD is on
> the motherboards Promise 20265 "raid" controller.
>
> > This would be a good question for the CD writing list,
> > cdwrite@other.debian.org.
>
> I tried that some time ago. So far, this is a sort of repetition of
> that. Joerg Schilling suggested that maybe I don't have DMA on or the
> reader and writer are on the same cable. Other discussion was off topic...
>
> In fact, I've also had this conversation from the other point of view
> with someone else, who was asking about this same problem in the finnish
> Linux group, sfnet.atk.linux. Now I have the same LG CD writer, the same
> VIA KT133A chipset, the same problem and the same discussion... I'd be
> amused if the problem weren't still unresolved.
>
> I decided to post here after I tried FreeBSD, didn't have a problem
> and thus it seemed likely that this is a Linux specific problem.
>
> I think I'll try to put together another system and see what happens
> there. I wonder if SGI's kernprof thing would be useful with this.
> I'll try that too, when I have the time.
> -
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--
Roger Larsson
Skellefteå
Sweden

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