Subject: Re: Throttling IO Requests in NetBSD via Congestion Control
To: Sumantra Kundu <>
From: Thor Lancelot Simon <>
List: tech-kern
Date: 08/21/2006 16:08:34
On Mon, Aug 21, 2006 at 02:53:42PM -0500, Sumantra Kundu wrote:
> >I guess I'm confused.  How, exactly, do we measure the maximum aggregate
> >operations/sec throughput of the disk?  There should be no upper bound
> >on the write throughput unless we reach that number, because writers
> >should never be put to sleep.  Is that not the case?
> >
> >This sort of issue is one reason why I suggested monitoring per-request
> >latency as the congestion metric, rather than merely using raw requests/sec
> >numbers.
> >
> We are indeed using and monitoring per process write request as a
> metric for measuring congestion. All processes are treated
> independently and are put to sleep whevener they are "observed"
> issuing write floods.....

I don't understand.  What is a "write flood"?  It is perfectly fine to
let any number of writes per second from a single process clear _except
in the case in which the disk is actually saturated_, and that case is
a _global_ condition, not a per-process one.