Darren Moffat,
Yes and no. A earlier statement within this discussion
was whether gzip is appropriate for .wav files. This just
gets a relative time to compress. And relative
sizes of the files after the compression.
My assumption is that gzip will run as a user app
in one environment. The normal r/w sys calls then take
a user buffer. So, it would be hard to believe that the
.wav file won't be read one user buff at at time. Yes,
it could be mmap'ed, but then it would have to be
unmapped. Too many sys calls, I think for the app.
Sorry, haven't looked at it for awhile..
Overall, I am just trying to guess at the read-ahead
delay versus the user buffer versus the internal fs.
The internal FS should take it basicly one FS block
at a time (or do multiple blocks in parallel)
and the user app takes it anywhere from
one buffer to one page size, 8k at a time. So, due
to reading one buffer at a time in a loop, with
a context switch from kernel to user each time. Thus,
I would expect that the gzip app would be sloooower.
So, my first step is to keep it simple (KISS)and tell
the group "what happens if" we do this simple
comparison? And how many bytes/sec is compressed?
And are they approx the same speed? Do you end up
with the same size file????
Mitchell Erblich
------------------
Darren J Moffat wrote:
>
> Erblichs wrote:
> > So, my first order would be to take 1GB or 10GB .wav files
> > AND time both the kernel implementation of Gzip and the
> > user application. Approx the same times MAY indicate
> > that the kernel implementation gzip funcs should
> > be treatedly maybe more as interactive scheduling
> > threads and that it is too high and blocks other
> > threads or proces from executing.
>
> If you just run gzip(1) against the files you are operating on the whole
> file so you only incur startup costs once and are thus doing quite a
> different compression to operating on a block level. A fairer
> comparison would be to build a userland program that compresses and then
> writes to disk in ZFS blocksize chunks, that way you are compressing the
> same sizes of data and doing the startup every time just like zio has to do.
>
> --
> Darren J Moffat
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