What's the story with DPC latency and 64-bit OSes?

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Qwerty69
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2009/05/16 19:54:23 (permalink)

What's the story with DPC latency and 64-bit OSes?

Hiyas -

What's the go with 64-bit operating systems - Vista x64, Windows 7 x64 or even Windows XP x64 - and DPC latency? I have been fiddling about with a couple of systems and comparing results back against 32-bit XP SP3. Ugly!!

Where I see about a 7us average DPC latency under Windows XP 32-bit, XP x64 is around 75us whereas Vista and Windows 7 RC-1 are both up around 150us with fairly consistent spikes. Even when disabling literally every device in device manager that isn't the motherboard, CPU or sound card and killing every service I can feasibly nuke, I can still get nowhere near the 7us average I see under Windows XP 32-bit edition.

Is this just an indicative symptom of a higher system load inherent in all 64-bit systems, is it symptomatic of less mature driver development under 64-bit environments or is this something all togeher different?

Anyone else experience similar issues or are you happily seeing equivalent results between 32-bit and 64-bit operating systems?

Cheers,

Q.
#1

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    Qwerty69
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    RE: What's the story with DPC latency and 64-bit OSes? 2009/05/19 11:27:26 (permalink)
    OK -

    An update on this issue...

    Seems like it was related to the motherboard, (irrespective of BIOS version). I have just moved to an AsRock x85 Deluxe from my old Asus P5W DH Deluxe and the DPC latency figures are virtually identical across XP x86, XP x64, Vista x64 and Windows 7 RC-1.

    Wow...

    Q.
    #2
    Jim Roseberry
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    RE: What's the story with DPC latency and 64-bit OSes? 2009/05/19 15:10:52 (permalink)
    You can get DPC latency fairly low in Vista (especially after some tweaks)... but it won't be quite as low as WinXP.
    DPC latency in Win7 will go a little lower than in Vista.
    post edited by Jim Roseberry - 2009/05/19 15:19:28

    Best Regards,

    Jim Roseberry
    jim@studiocat.com
    www.studiocat.com
    #3
    Qwerty69
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    RE: What's the story with DPC latency and 64-bit OSes? 2009/05/19 17:56:28 (permalink)
    That was the weird thing Jim - with the older motherboard, I tweaked and tweaked and tweaked AND physically disabled a bunch of devices and still couldn't get anywhere near XP, (XP averaged around 5 microseconds, Vista was 175-ish with everything disabled).

    With the new X58 deluxe board and an i7 920, XP sits at 4 microseconds, Vista is at 10 and Win 7 is 7 microseconds => all OS'es jam-packed and not optimised at all, (ie. all services running + anti-virus etc.).

    That makes me think there was some kind of issue with the driver support or BIOS code under 64-bit operating systems when using the Asus P5W DH Deluxe board.

    Ciao,

    Q.
    post edited by Qwerty69 - 2009/05/19 18:06:12
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    Brandon Ryan [Roland]
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    RE: What's the story with DPC latency and 64-bit OSes? 2009/05/19 22:34:00 (permalink)
    BIOS and drivers can make ALL the difference when it comes to Vista's DPC latency and subsequently its performance as a DAW. This cannot be underestimated.

    For example: On one machine, I merely updated a LAN driver (which needed to be disabled before) and seen Vista's DPC latency go from an erratic 100-ish to a solid 30 or 40-something.

    "The sky above the port was the color of television, tuned to a dead channel." WG

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    #5
    Qwerty69
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    RE: What's the story with DPC latency and 64-bit OSes? 2009/05/19 22:55:41 (permalink)
    Yep - it befuddles me how on that Asus board XP 32-bit could be so rock solid and anything else so pear-shaped...

    Ah well - all's well, that ends well. This new machine is astoundingly quick, (but I'm sure I said that when I got my first 286 too...)!

    Ciao,

    Q.
    #6
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