Messages in this thread | | | Date | Mon, 17 Oct 2005 02:41:40 -0700 (PDT) | From | li nux <> | Subject | Re: A problem about DIRECT IO on ext3 |
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--- Jens Axboe <axboe@suse.de> wrote:
> On Mon, Oct 17 2005, Grzegorz Kulewski wrote: > > On Mon, 17 Oct 2005, Jens Axboe wrote: > > >>how to correct this problem ? > > > > > >See your buffer address, it's not aligned. You > need to align that as > > >well. This is needed because the hardware will > dma directly to the user > > >buffer, and to be on the safe side we require the > same alignment as the > > >block layer will normally generate for file > system io. > > > > > >So in short, just align your read buffer to the > same as your block size > > >and you will be fine. Example: > > > > > >#define BS (4096) > > >#define MASK (BS - 1) > > >#define ALIGN(buf) (((unsigned long) (buf) + > MASK) & ~(MASK)) > > > > > >char *ptr = malloc(BS + MASK); > > >char *buf = (char *) ALIGN(ptr); > > > > > >read(fd, buf, BS); > > > > Shouldn't one use posix_memalign(3) for that? > > Dunno if one 'should', one 'can' if one wants to. I > prefer to do it > manually so I don't have to jump through #define > hoops to get at it > (which, btw, still doesn't expose it on this > machine). > > -- > Jens Axboe
Thanx a lot Jens :-) Its working now. I did not have to make these adjustments on 2.6 Is looks to be having more relaxation.
Can somebody please throw some light on how to find your system's hard/soft block size ?
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