Re: threadlets as 'naive pool of threads', epoll, some measurements

Ingo Molnar
2007-02-26T12:57:17Z

* Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:

> > yet another performance update - with the fixed 'heaps of stupid
> > threads' evserver_threadlet.c code attached below i got:
> >
> > > evserver_epoll: 9400 reqs/sec
> > > evserver_epoll_threadlet: 9400 reqs/sec
> >
> > evserver_threadlet: 9000 reqs/sec
> >
> > so the overhead, instead of the 10x slowdown Evgeniy
> > predicted/feared, is 4% for this particular, very event-centric
> > workload.
> >
> > why? because Evgeniy still overlooks what i've mentioned so many
> > times: that there is lots of inherent 'caching' possible even in
> > this particular '8000 clients' workload, which even the most stupid
> > threadlet queueing model is able to take advantage of. The maximum
> > level of parallelism that i've measured during this test was 161
> > threads.
>
> :)
>
> I feared _ONLY_ situation when thousands of thereads are eating my
> brain - so case when 161 threads are running simultanesoulsy is not
> that bad compared to what micro-design can do (of its best/worst) at
> all!

even with ten thousand threads it is still pretty fast. Certainly not
'10 times slower' as you claimed. And it takes only a single, trivial
outer event loop to lift it up to the performance levels of a pure event
based server.

conclusion: currently i dont see a compelling need for the kevents
subsystem. epoll is a pretty nice API and it covers most of the event
sources and nicely builds upon our existing poll() infrastructure.

furthermore, i very much contest your claim that a high-performance,
highly scalable webserver needs a kevent+nonblock design. Even if i
ignore all the obvious usability and maintainance-cost advantages of
threadlets.

> So, caching is good - threadlets do not spawn a new thread, kevent
> returns immediately, but in case of things are not that shine -
> threadlets spawnd a new thread, while kevent process next request or
> waits for all completed.

no. Please read the evserver_threadlet.c code. There's no kevent in
there. There's no epoll() in there. All that you can see there is the
natural behavior of pure threadlets. And it's not a workload /I/ picked
for threadlets - it is a workload, filesize, parallelism level and
request handling function /you/ picked for "event-servers".

Ingo