🚀 go-pugleaf

fl@tools.de (Frank Lancaster) writes:

>>   That is, I
>>   get the impression that setting a large value for ADFSBuffers will NOT
>>   have ANY effect on a SINGLE file, but using (e.g.) 256 buffers will allow
>>   up to 256 files to be buffered simultaneously.

>Actually adfsbuffers does have a dramatic effect on reading
>and writing a single file. Using my RISC OS tar for a large hard disc
>backup with compression, I normally set adfsbuffers to 255. Then
>writing to the disc happens in the background and the compression
>of a file can begin before the preceeding file has been completely
>written to disc. This also works under taskwindows, so you get
>somewhat better preemptive multitasking.

... you don't think, perhaps, that the significant improvement is due to
the fact that you are reading multiple files and writing to 1? And
that the more buffers you have, the more files can be buffered before
buffers have to be flushed?
Remember that read-buffers should make a difference if you're using a
FS that supoprts read-ahead...

Perhaps ADFSBuffers IS able to use more than 1 "1kB buffer" on a single
file (i.e. actually use a 256kB write buffer for a single file), but this
is not aparrent from the help on the configure option...

(Also, I would think that tar would be slightly different anyway, as it's
a C program, and if it uses stdio then it's likely that C would be
providing buffers, in which case, I would assume you're using setvbuf()
to allocate large I/O buffers in order to improve the throughput...)

Also, I have found with that sort of disc operation (reading, writing are
interleaved a lot) that a slight increase in buffer size can be all that
is needed to drop below the 'thrashing' threshold, and the amount of seeking
necessary drops considerably, thus speeding up the process a lot.
(With !CBAdecode, the difference between 4kB buffers and 16kB is amazing)
-- 
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