[Mono-list] Mod-mono-server using too much CPU, running too many times

Joshua Tauberer tauberer@for.net
Fri, 01 Oct 2004 17:02:40 -0400

Gonzalo Paniagua Javier wrote:
> That's likely to happen if you use the managed file system watcher, not
> with FAM, for large directories (many files)

FAM was failing on FAMOpen.  I read somewhere that portmap has to be 
running for FAM to work, which it wasn't.  But even after starting 
portmap and xinetd it still falls back on the managed watcher.

I made two changes to the managed watcher, and for now Mono is humbly
using 0.0-0.1% cpu while it's idle.  Firstly, I set the update delay to 
be 50 times the time it took to scan for changes (with a lower and upper
bound).  This helped, but even while the site was only chaching about 6
files, every few seconds Mono would spike a few percent in cpu usage.

Then I thought that the scan for changes might be faster if Mono did not
have to iterate through the contents of directories.  It has to do this
if there's a wildcard in the mask, but if the mask is just a filename,
as is (always?) the case for caching, checking whether that file exists
directly might be faster.  So, I have it always check with File.Exists
for the file, and only if that fails does it use 
Directory.GetFileSystemEntries.  If there are wildcards, File.Exists 
should, I think, always return false, so that's fine, but I haven't 
tested it.

My unscientific benchmarks show that using
Directory.GetFileSystemEntries takes ~0.003 seconds per call, for
directories with only a small number of files and with a file mask with
no wildcards.  Calling File.Exists only takes ~0.0001 seconds.  I'm
skeptical that this is what is actually helping -- they're such small 

>>2)  How does mod_mono work in relation to Apache's prefork module?
> That used to happen if you get a few requests when mod_mono has not
> started mod-mono-server for the first time. After the burst only one of
> those mono instances is really used. I'll file a bug report about this
> and fix it.

Also I'm getting a few defunct mono's laying around (which disappear on 
an httpd restart).

Thanks for your explanations, Gonzalo!

- Joshua Tauberer


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