Re: Disc cache worth it?

On 2014-06-25 12:57, Rob Kendrick wrote:
> On Wed, Jun 25, 2014 at 12:14:16PM +0100, george greenfield wrote:
>
>> Does that mean that selecting 'Make file operations multitask' in
>> !Configure-Filer, actually doesn't?
>
> It means that it writes smaller chunks and calls Wimp_Poll in between
> them
> to give other applications a chance, at the expense of expediency.
> The
> whole system stops while the individual chunks are written, being
> accepted by FileSwitch, which then in turn passes them to the
> handling
> file system (most likely FileCore), which then hands them to the
> block
> device driver (ADFS, IDEFS, SDFS, etc), percolating the
> success/failure
> result back up the stack to the application.

I think there are a couple of errors in that explanation.

First of all, IIRC ticking that option only affects FilerAction. This
is a
desktop facility for doing multitasking operations on files and
directories
(such as copy, move, delete, etc) with a window opening to show
progress.

Unticking that option causes these operations to revert to using the
single-tasking command line equivalents for these operations (e.g.
*copy)
which could end up being faster at the expense that your desktop stops
multitasking.

Secondly, it's not true to say file system operations block everything
in RISC OS - some file systems (notably ADFS) implement "background
transfers" which allow much of RISC OS to continue to operate while the
underlying file operation runs (e.g. via DMA or some such). However,
many
file systems _don't_ implement background transfers - e.g. SDFS - so
these will hog the system for the duration of the low-level operation.

Adding background transfers to SDFS has always been on the roadmap but
it's a lot of work; implementing background transfers on RISC OS is a
particularly tricky task and SDFS is complex enough already for various
reasons. It is hoped that one of the later stages of "filesystem
improvements" that we've been hosting bounties about on the ROOL site
will address some of these issues, but at the current rate that the
bounty scheme has been gathering donations, we'll all be dead and gone
before any of that work happens.

Ta,

Steve