[wdmaudiodev] Re: AW: Re: Already got cool latency figures - how about everyone else?
- From: "Jeff Pages" <jeff@xxxxxxxxxxxxxxxx>
- To: <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Wed, 29 Jan 2003 10:43:55 +1100
I have seen latency times at DISPATCH_LEVEL of greater than 10ms under XP
when certain devices are running, most notably CDROM drives. At DIRQL I'm
typically seeing latencies of the order of 10us under 2000 and XP, but on
one of my test machines running 98 and ME I have seen hardware interrupt
latencies of many milliseconds.
Jeff
----- Original Message -----
From: "Van Mieghem, Dirk" <dvm@xxxxxxxx>
To: <wdmaudiodev@xxxxxxxxxxxxx>
Sent: Wednesday, January 29, 2003 5:32 AM
Subject: [wdmaudiodev] Re: AW: Re: Already got cool latency figures - how
about everyone else?
>
> Hi Tobias,
> in an NT based kernel a ready thread with the highest priority is
scheduled
> immediately without any fixed timing limitation. It doesn't matter if this
> thread is running in user or kernel mode either. The problem is that
> scheduling is only enabled if the current IRQL is below dispatch level.
ANY
> driver that spends too much time at elevated IRQL (ISR, DPC,...) will
> prevent all threads from running. Typically, this latency is well below
1ms,
> even below 10us. However, in an audio driver it's the worst case scenario
> that counts. IOW, this worst case latency depends on the behavior of the
> complete set of active drivers, not that much on the speed of the CPU. If
a
> driver chooses to wait for its hardware at a high IRQL for 1ms or more, it
> doesn't matter if the CPU is running at 100MHz or 3GHz, the worst case
> latency will be at least 1ms.
>
> Best regards,
> Dirk
>
> > So - in times of processors gaining 3 GHz and more,
> > wouldn't it be wise to have a task scheduler at
> > 5khz or 10khz? Should be just a define in the
> > kernel, if designed well...
> >
> > Best would be to be able to tweak this via registry,
> > so one can decide if performance for longer-running
> > processes is important or better realtime-response...
> >
> > Tobias
> > ******************
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>
>
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