Re: cdrom changes in test13-pre2 slow down cdrom access by 70%

From: Jens Axboe (axboe@suse.de)
Date: Sat Dec 23 2000 - 07:37:37 EST

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    On Fri, Dec 22 2000, David Mansfield wrote:
    > Jens,
    >
    > The cdrom changes that went into test13-pre2 really kill the performance
    > of my cdrom. I'm using cdparanoia to read audio data, and it normally
    > reads at 2-3x. Since test13-pre2 it's down to .6 - .7x. I've reverted
    > the following files to the ones from test13-pre1 and it's back to
    > normal:

    Humm, interesting.

    > This is a huge patch, is there some way I could break it apart to see
    > what the relevant changes are?

    The change affecting you is most likely the CDROMREADAUDIO change,
    where we now just read a single cdda frame at the time. This gives
    us less data per interrupt, and apparently this is more than a
    theoretical slowdown for you. Please try with attached patch. If
    this solves it (as it should), then we should probably try and do
    persistent allocation of a bigger buffer for things like this.
    Grabbing > 1 frame was disabled because multi-page allocation is not
    reliable.

    --- drivers/cdrom/cdrom.c~ Sat Dec 23 13:27:33 2000
    +++ drivers/cdrom/cdrom.c Sat Dec 23 13:30:39 2000
    @@ -1985,7 +1985,7 @@
                     }
             case CDROMREADAUDIO: {
                     struct cdrom_read_audio ra;
    - int lba;
    + int lba, frames;
     
                     IOCTL_IN(arg, struct cdrom_read_audio, ra);
     
    @@ -2002,7 +2002,9 @@
                     if (lba < 0 || ra.nframes <= 0)
                             return -EINVAL;
     
    - if ((cgc.buffer = (char *) kmalloc(CD_FRAMESIZE_RAW, GFP_KERNEL)) == NULL)
    + frames = ra.nframes > 8 ? 8 : ra.nframes;
    +
    + if ((cgc.buffer = (char *) kmalloc(CD_FRAMESIZE_RAW * frames, GFP_KERNEL)) == NULL)
                             return -ENOMEM;
     
                     if (!access_ok(VERIFY_WRITE, ra.buf, ra.nframes*CD_FRAMESIZE_RAW)) {
    @@ -2011,12 +2013,14 @@
                     }
                     cgc.data_direction = CGC_DATA_READ;
                     while (ra.nframes > 0) {
    - ret = cdrom_read_block(cdi, &cgc, lba, 1, 1, CD_FRAMESIZE_RAW);
    - if (ret) break;
    - __copy_to_user(ra.buf, cgc.buffer, CD_FRAMESIZE_RAW);
    - ra.buf += CD_FRAMESIZE_RAW;
    - ra.nframes--;
    - lba++;
    + ret = cdrom_read_block(cdi, &cgc, lba, frames, 1, CD_FRAMESIZE_RAW);
    + if (ret)
    + break;
    + __copy_to_user(ra.buf, cgc.buffer,
    + CD_FRAMESIZE_RAW * frames);
    + ra.buf += (CD_FRAMESIZE_RAW * frames);
    + ra.nframes -= frames;
    + lba += frames;
                     }
                     kfree(cgc.buffer);
                     return ret; 

    -- 
* Jens Axboe <axboe@suse.de>
* SuSE Labs
-
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