Re: DMA transfers in 2.5.67

From: Chuck Ebbert (76306.1226@compuserve.com)
Date: Fri Apr 18 2003 - 06:25:46 EST


Andrew Morton wrote:

> > Chuck Ebbert <76306.1226@compuserve.com> wrote:
> > >
> > > # mount /ext3_fs
> > > # time dd if=/ext3_fs/100MiB_file of=/dev/null bs=32k
> > >
> > > 2.4.20aa1 : 3.3 sec (exactly what I expect to see)
> > > 2.5.66 : 6.6 sec
> >
> > With this test 2.4 will leave a lot more unwritten dirty data in memory.
> >
> > You should include a `sync' in the timings.
>
> Well you should include the sync if you're writing to disk ;)

  :)

  All is not beer and skittles here with Andrea's kernel, though.
Sometimes instead of 31MB/sec I get this with 1 sequential stream:

 1 0 0 0 1232 1120 47988 0 0 14928 0 3834 7534 1 44 55
 1 0 0 0 1372 1120 47848 0 0 14704 0 3778 7446 0 32 68
 1 0 0 0 1464 1064 47816 0 0 14880 0 3822 7501 1 43 56
 1 0 0 0 1336 1064 47944 0 0 14844 0 3813 7493 0 29 71
 1 0 0 0 1432 1064 47848 0 0 14748 32 3800 7467 0 41 59
 1 0 0 0 1532 1064 47748 0 0 13976 0 3596 7045 1 33 66
 

  Pretty high context switch and interrupt rates for a PPro 200, huh?

  And I can't reliably reproduce it (so far...)

------
 Chuck
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