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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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