Andrea Arcangeli wrote:
>
> On Wed, Jan 24, 2001 at 04:05:12PM +0100, Sasi Peter wrote:
> > > This isn't obvious. Your working may not fit in cache and so the kernel
> > > understand it's worthless to swapout stuff to make space to a polluted
> > > cache.
> >
> > But your understanding agrees on that the larger chunks for each stream
> > we read into cache, the more efficient for this kind of RAID disk
> > structure the read is, thus basically the more cache we have, the more
> > bandwidth we can serve. (disks give more data in the same time with
> > fewer long reads than with several shorter ones)
>
> The size of the I/O requests doesn't grow linearly with with the size of the
> cache, as far as you have some mbyte of cache you will also be able to sumbit
> full sized requests to disk (512K per req on 2.4). In your workload you just
> had enough memory for the readahead.
>
> In general if your working set doesn't fit in cache, the size of the cache is
> unrelated to the bandwith you get out of your RAID, infact if your working set
> doesn't fit in cache you should not pass through the cache at all to get the
> best performance and to save CPU cycles and L1 dcache and L2 cache (O_DIRECT).
>
This may be a bit OT, but when you say O_DIRECT, that implies that you
can pass that flag to open(2) and it will bypass the page cache, and
read directly into user-space buffers (zero-copy IO)? Does this also
bypass the read-ahead mechanisms in the kernel? Does it imply O_SYNC?
Lots of questions... no answers. Sigh.
David
--
David Mansfield (718) 963-2020
[email protected]
Ultramaster Group, LLC http://www.ultramaster.com
Can 2.2.x linux made to boot from an ide zip drive? If so, what is required?
DB
On Fri, 16 Feb 2001, Dennis wrote:
> Can 2.2.x linux made to boot from an ide zip drive? If so, what is required?
There is a (rather old, but sufficient) mini-HOWTO about this. I use it to
create a Linux-From-Scratch with RPMs. The url is:
http://www.linuxdoc.org/HOWTO/mini/Zip-Install.html
--
Sven Vermeulen
On Fri, 16 Feb 2001, Dennis wrote:
> Can 2.2.x linux made to boot from an ide zip drive? If so, what is required?
Oops, sorry, wrong URL (damned):
http://www.linuxdoc.org/HOWTO/mini/Install-From-ZIP.html
Found it with google ("zip install linux mini"). Just to make sure that,
if it's the wrong URL again (but I doubt it), it's easy to find yourself.
--
Sven Vermeulen