I agree with you that it may be an overkill to poll that fast, but when you
have such a big slowdown - from 2ms to 15 ms - I don’t know, I would like to
know the exact cause. It could bite me again somewhere else where I actually
do need the speed !
Alberto.
-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com]On Behalf Of Chuck Batson
Sent: Friday, July 30, 2004 10:50 AM
To: Windows System Software Devs Interest List
Subject: Re: [ntdev] Windows 2000 High Resolution Timer
1,000 CPU cycles does not necessarily equate to 1,000 instructions. But
I see your point. Even if it was an order of magnitude higher (how many
cycles exactly is the overhead for an ISR on Windows?), that’s still
only half a percent. It still seems like 500 times per second is
overkill (perhaps my age showing). Then again, it is MY computer,
right? I don’t want some random driver writer dictating how my CPU
cycles are spent, any more than you want an OS that prevents you from
reading PCI config space. 
Chuck
----- Original Message -----
From: “Moreira, Alberto”
To: “Windows System Software Devs Interest List”
Sent: Friday, July 30, 2004 8:45 PM
Subject: RE: [ntdev] Windows 2000 High Resolution Timer
> Golly, guys, polling every 2ms is nothing to a fast processor. Say you
spend
> 1,000 instructions to handle it, that’s 1K/2M = .05 % of the CPU
bandwidth.
> Piece of cake. Or at least it should be. If it isn’t, something in
between
> isn’t performing up to snuff. Time to get that scope out ?
>
> Alberto.
>
>
> -----Original Message-----
> From: xxxxx@lists.osr.com
> [mailto:xxxxx@lists.osr.com]On Behalf Of Chuck Batson
> Sent: Friday, July 30, 2004 5:50 AM
> To: Windows System Software Devs Interest List
> Subject: Re: [ntdev] Windows 2000 High Resolution Timer
>
>
> Is this for a commercial product, or for your own amusement? I’m no
> expert, but my gut tells me polling a device 500 times per second is
> excessive. That’s every 2 million CPU cycles on a 1GHz machine, not
to
> mention the cycles your ISR or polling routine will eat up. Viewed
> another way, that’s one poll for every 120,000 bytes at full USB 2.0
> bandwidth. If the design of your “high speed” device depends on
Windows
> polling at a rate of 500 times per second, you’ve probably already
lost
> the battle as far as “high speed” goes. You’ll likely get better
> results putting a big buffer on the device and polling less
frequently.
>
> Chuck
>
> ----- Original Message -----
> From: “Manohara.K”
> Newsgroups: ntdev
> To: “Windows System Software Devs Interest List”
> Sent: Friday, July 30, 2004 3:58 PM
> Subject: [ntdev] Windows 2000 High Resolution Timer
>
>
> > Hi,
> >
> > I am working on High Speed USB Data aqusition Device.
> > Iam want to poll my device every 2 milli second.Iam currently trying
> to use
> > KeInitializeTimer. On testign the DPC attached to the timer is
> > called only every 15 milli seconds on a Winodws 2000 - SP4 - 2.6 Ghz
> > Machine.
> > Has any one noticed this behaviour?.I dont want to use
> ExSetTimerResolution.
> > Is there any other method where I can increase my Timer Resolution /
> polling
> > routine resolution.
> > Is there any other technique to achieve this .
> >
> > Regards,
> >
> > Manohara
—
Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256
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