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From Plüm, Rüdiger, Vodafone Group <ruediger.pl...@vodafone.com>
Subject AW: httpd 2.4.25, mpm_event, ssl: Status of async write completion?
Date Thu, 02 Feb 2017 12:44:55 GMT


> -----Ursprüngliche Nachricht-----
> Von: Niklas Edmundsson [mailto:nikke@acc.umu.se]
> Gesendet: Donnerstag, 2. Februar 2017 13:31
> An: httpd-dev <dev@httpd.apache.org>
> Betreff: httpd 2.4.25, mpm_event, ssl: Status of async write completion?
> 
> 
> Hi all!
> 
> As we're seeing more and more https on ftp.acc.umu.se I've noticed
> that the number of threads listed as state W in server-status has
> skyrocketed.
> 
> From 2-4 threads busy using http we're talking 70-100 threads for the
> same bandwidth when the machine is pushing a mighty 2.7% average CPU
> load.
> 
> This is on a large-file workload, serving plain files.
> 
> I anticipated a few more threads due to ssl, but for slow downloaders
> I would expect connections doing async write and mostly waiting for
> the bits to dribble through the Internet Tubes inbetween the
> occational wakeup to do ssl&send...
> 
> Are we not doing async write completion at all on https/ssl and
> falling back to the old worker behaviour of one thread per connection?


We do async with SSL as well, but in a worse way than http with static resources. For static
resources
in the form of files we can deliver the whole thing async without switching
back to sync with http. For SSL we are in sync mode each time we need to encrypt. Only encrypted
data that cannot be sent immediately is sent async.

So the increase you see can be said to be expected. Trunk has approaches to overcome this,
though there
has been reported that there are still some bugs with it.

Regards

Rüdiger


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