On Tue, 16 May 2000, Pasi Kärkkäinen wrote:
(snip)
> >
> Sorry, this was my mistake. I had forgotten to enable automatic DMA turn
> on on 2.3.99-pre6.
>
> Now when the dma is automatically turn on, the fscks are fast again. I
> still wonder, why is fsck so *slow* when the dma is not turned on?
>
> When the dma is not on, fsck reads from the disk, "waits" ~5 seconds,
> then again reads, waits ~5 seconds and so on..
Basically, without DMA, the kernel has to move the data itself, using the
processor; while it's doing this, fsck is in a "waiting" state, rather
than running. DMA enables the two actions to be performed simultaneously,
cutting the CPU overhead significantly.
I would guess that other performance tweaks are also enabled by switching
on DMA mode; otherwise, the performance hit is just too dramatic to be
explained in this way, I think?
James.
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This archive was generated by hypermail 2b29 : Tue May 23 2000 - 21:00:11 EST