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

From: Suparna Bhattacharya
Date: Thu Feb 22 2007 - 09:13:32 EST

On Thu, Feb 22, 2007 at 01:59:31PM +0100, Ingo Molnar wrote:
> * Evgeniy Polyakov <johnpol@xxxxxxxxxxx> 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.)

At what point are the cachemiss threads destroyed ? In other words how well
does this adapt to load variations ? For example, would this 80MB of RAM
continue to be locked down even during periods of lighter loads thereafter ?


> > 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

Suparna Bhattacharya (suparna@xxxxxxxxxx)
Linux Technology Center
IBM Software Lab, India

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