Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

Ingo Molnar
2007-02-22T13:04:54Z

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

> It is not a TUX anymore - you had 1024 threads, and all of them will
> be consumed by tcp_sendmsg() for slow clients - rescheduling will kill
> a machine.

maybe it will, maybe it wont. Lets try? There is no true difference
between having a 'request structure' that represents the current state
of the HTTP connection plus a statemachine that moves that request
between various queues, and a 'kernel stack' that goes in and out of
runnable state and carries its processing state in its stack - other
than the amount of RAM they take. (the kernel stack is 4K at a minimum -
so with a million outstanding requests they would use up 4 GB of RAM.
With 20k outstanding requests it's 80 MB of RAM - that's acceptable.)

> My tests show that with 4k connections per second (8k concurrency)
> more than 20k connections of 80k total block in tcp_sendmsg() over
> gigabit lan between quite fast machines.

yeah. Note that you can have a million sleeping threads if you want, the
scheduler wont care. What matters more is the amount of true concurrency
that is present at any given time. But yes, i agree that overscheduling
can be a problem.

btw., what is the measurement utility you are using with kevents ('ab'
perhaps, with a high -c concurrency count?), and which webserver are you
using? (light-httpd?)

Ingo