Re: Determining disk activity per volume
Re: Determining disk activity per volume
- Subject: Re: Determining disk activity per volume
- From: Michael Cashwell <email@hidden>
- Date: Wed, 11 Oct 2006 09:52:50 -0400
On Oct 11, 2006, at 3:36 AM, Michael Smith wrote:
On Oct 10, 2006, at 10:19 PM, Arvind Dalvi wrote:
how about developing I/O Media Filter? "An I/O Media Object acts
as a channel for all I/O that goes to the
storage underlying it"
http://lists.apple.com/archives/Darwin-development/2002/May/
msg00382.html
Again, this puts you on the hot path for potentially thousands of
operations a second, to update a UI at a fraction of that rate.
Unless you are trying to gather statistics that aren't otherwise
available, not a good idea.
Granted, if the info were otherwise available then adding anything to
the hot-path would be wasteful.
But if the only thing such an IOMedia filter did was accumulate the
amount of data read and written as the commands flew by and then (at
a much slower pace) provided those sums when requested by a userland
UI component it shouldn't be overly expensive.
The actual additional hot-path code is a couple of atomic adds. So as
long as the layering infrastructure itself is not heavyweight then it
should be acceptable. If adding just a NOP-layer is too expensive
then there's a more fundamental problem.
Also, to be fair, the rate that IO commands go by has nothing to do
with the update rate in the UI. The hot-path would not trigger or
invoke UI updates. It would only accumulate their sizes.
-Mike
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