[OpenAFS] Re: Openafs performance with Apache/PHP
Mon, 13 Aug 2007 19:03:08 -0500
On 8/13/07, Russ Allbery <email@example.com> wrote:
> That -daemons value is way too high and will cause a ton of context
> switches, so that isn't what you want. However, it sounded like you'd
> already tried tweaking that. See the afsd man page:
> The default number of background daemons is two, enough to service
> at least five simultaneous users of the machine. To increase the
> number, use the -daemons argument. A value greater than six is not
> generally necessary.
> That's the first thing I'd reduce if you're seeing an insane number of
> context switches.
So I must have missed that chunk of the docs... I had tried dropping
it down to 10 before and that didn't help the situation, I dropped it
down to 6 and the performance degradation finally levels off at 8
requests per second. Context switches also dropped some, but still
hover around 220,000 when I'm hitting it with 30 users. So this is at
least a partial solution to my problem.
> Other than that, I looked at the original message and thought "oh, that's
> interesting" but I didn't really have any useful feedback. Have you seen
> jhutz's document on cache tuning? It's probably the best place to start
> just to make sure that the cache values are generally reasonable and
> consistent with your working set and cache size.
I've looked through it before, but I usually get too annoyed when the
asfd process kernel panics my machine if I get dcache/stats too high.
My webservers deal with an annoying large volume of content (~35GB)
and defining a working set size seems to be a moving target to say the
least, but I'll take another stab at it.
> Certainly, if Arla is scaling, using Arla is a valid option. I'm curious
> on improving OpenAFS to match, of course, but Arla uses a considerably
> different kernel architecture and I can see some theoretical reasons why
> it might scale better under certain loads.
Unfortunately there are other issues preventing me from using arla,
and I do realize that its almost like comparing apples to oranges as
far as internals go. It simply degraded how I would expect it to
degrade. This is the real crux of the problem I'm running into
Thank you all very much for the feedback.
If the database server goes down and there is no code to hear it, does
it really go down?