Re: What is a CACHE_HIT event in fs_usage?
Re: What is a CACHE_HIT event in fs_usage?
- Subject: Re: What is a CACHE_HIT event in fs_usage?
- From: Quinn <email@hidden>
- Date: Tue, 1 Feb 2005 06:54:07 +0000
At 10:00 -0800 7/1/05, Richard Jackson wrote:
I'm using the "fs_usage" utility to help me optimize my
application's I/O calls, and I see a lot of events labeled
"CACHE_HIT". Could someone explain what these are? (VM paging? File
System caching?)
This corresponds to the symbol DBG_CACHE_HIT_FAULT. It indicates
that the process took a page fault but the page was found in the
cache. [Mac OS X has a Unified Buffer Cache (between the file system
and VM), so there's no distinction between VM and file system cache.]
This is in contrast to "PAGE_IN" (DBG_PAGEIN_FAULT) which indicates
that the system took a page fault that required a read from disk.
To understand the exact logic, take a look at the vm_fault routine in
"xnu/osfmk/vm/vm_fault.c".
S+E
--
Quinn "The Eskimo!" <http://www.apple.com/developer/>
Apple Developer Technical Support * Networking, Communications, Hardware
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