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Date:      Tue, 22 Apr 2008 22:34:14 +0200
From:      Ivan Voras <ivoras@freebsd.org>
To:        freebsd-current@freebsd.org
Subject:   Re: Http Accept filters (accf_http)
Message-ID:  <fuli49$pa3$1@ger.gmane.org>
In-Reply-To: <480E3E66.3000303@samsco.org>
References:  <8481.1208889581@critter.freebsd.dk> <480E3E66.3000303@samsco.org>

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Scott Long wrote:
> Poul-Henning Kamp wrote:
>> In message <480E307B.901@quis.cx>, Jille writes:
>>> Hello,
>>>
>>> I've read about accf_http(9) some time ago, and I was wondering about=
=20
>>> it's performance.
>>> Does it increase performance on all workloads ?
>>> (I'm intrested in the improvements for a PHP-apache-webserver with=20
>>> about 50 request/second average.)
>>
>> I doubt you will see measurable performance difference from using
>> request filters at such low traffic.
>>
>=20
> The accept filters do reduce service latency and probably have a small
> benefit in CPU utilization.  50 requests/sec is probably enough to see
> a benefit for something like PHP or PERL.  It definitely won't hurt, an=
d
> even if there's no measurable benefit now, it'll help prepare you for
> scaling in the future.

Does anyone know why accf_accept is disabled by default in the ports'=20
stock Apache 2.2 (it's disabled in the default config files)? I thought=20
it was because it was dangerous or flawed for some reason, though (at=20
least for light loads comparable to those of OP) it seems to work fine.

As to the original question: theoretically it could help requests for=20
images and similar small objects - PHP scripts execute too long for the=20
benefits to be visible. In my own case, though, I couldn't discern a=20
difference with and without accf_httpd. One other thing is that=20
keepalives essentially nullify the effects of the filter (as far as I=20
understand, the filter only works on the first bytes after the=20
connection is established), but keepalives can help performance much=20
more than accfs.


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