Messages in this thread | | | Date | Thu, 29 May 2003 19:33:25 +0200 | From | Jens Axboe <> | Subject | Re: 2.5.69-70 ide-cd to guarantee fault-free CD/DVD burning experience? |
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On Thu, May 29 2003, Andy Polyakov wrote: > > > ... I noticed that DMA is never engaged > > > on that buffer allocated with kmalloc. The question is if it's > > > intentional? If answer is yes, then the case is dismissed. If not, then > > > it should be looked into... > > > > Depends on the lower level driver, for ide-cd yes kmalloc'ed data will > > not be dma'ed to. We require a valid bio setup for that, usually the bio > > mapping will fail exactly because the length/alignment isn't correct for > > ide-cd. > > > > > ... it might be appropriate to retry > > > bio_map_user on buffer. I'm actually stepping out of my competence > > > domains here... > > > > It's usually not worth it. If the buffer is < 4 bytes, we don't dma. Big > > deal. > > Well, I'm concerned rather about cases when user buffer ends up in non > DMA-able memory than small or misaligned buffers. I mean those who have > system with loads of RAM didn't do anything wrong, yet they get > "punished." But I'm not actually insisting! Just saying that it *might* > be worth reconsidering "ide-cd won't do dma without bio setup" clause or > retry bio_map_user on kalloc-ed buffer. At least for transfers not > smaller than say 2K:-)
This is bogus. Applications already dish out the right buffers and in the right lengths. It's the logical thing to do.
You are making up a problem that doesn't exist.
-- Jens Axboe
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