Re: Poor floppy performance in kernel 2.4.10
Ville Herva (firstname.lastname@example.org)
Thu, 18 Oct 2001 19:17:32 +0300
On Thu, Oct 18, 2001 at 05:42:44PM +0200, you [Kamil Iskra] claimed:
> On Thu, 18 Oct 2001, Andreas Dilger wrote:
> > > The behaviour is as if no caching was done,
> > > there is a slowdown by a factor of two.
> > I think this is a result of the "blockdev in pagecache" change added in
> > 2.4.10. One of the byproducts of this change is that if a block device
> > is closed (no other openers) then all of the pages from this device are
> > dropped from the cache. In the case of a floppy drive, this is very
> > important, as you don't want to be cacheing data from one floppy after
> > you have inserted a new floppy.
> > In contrast, if you mounted the floppy instead of using mtools, it would
> > probably have good performance for small files as well.
> That's very interesting. It would explain why it takes 2 seconds _every_
> time you invoke "mdir", whereas before the invocations after the first one
> were more or less instantenous. And indeed, as you say, mounting a floppy
> does result in a good performance.
> However, it does not explain why the first invocation is two times slower
> (it's 1 sec with kernel 2.4.9 and 2 secs with 2.4.10, the effect is even
> more visible for mcopy of a small file, like 30KB). I strace'd mdir and
> it's opening /dev/fd0 just once, at the beginning, and closing it at the
That's propably beacause it syncs the writes on close().
Perhaps you could try the trick Linus suggested in another thread, namely:
sleep 1000 < /dev/fd0 &
That keeps one (dummy) reference to the floppy device open until you're done
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