[wdmaudiodev] Audio stack in 32-bit Vista VM guest is MUCH slower than in 64-bit Vista guest

  • From: Eugene Muzychenko <emuzychenko@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Tue, 5 Aug 2008 16:58:51 +0700


To debug my kernel-mode code, I use several VMs under VMware
Workstation (now 6.0.4 but no difference since 5.5) - Windows 2000, XP
(32 and 64-bit), 2003 (32-bit), Vista (32 and 64-bit). I noticed that
32-bit Vista guest works MUCH slower than all other OSes, regardless
of their bitness. All other OSes, including 64-bit Vista, have good
performance; 64-bit Vista is slower, of course, but 32-bit Vista is
VERY slow.

I have an old desktop (Athlon 64 X2 3800+, 2.2 GHz, Hitachi
HDT722525DLA380, 7200, SATA II/NCQ, 50 MB/s avg read, 14 ms seek) and
a new notebook (Acer Aspire 4920G, T8300, 2.4 GHz, WD3200BEVT, 5400,
SATA II/NCQ, 55 MB/s avg read, 17 ms seek)

If I run audio player (WinAMP, Foobar2000) in 64-bit Vista guest (as
in Win2000/XP/2003 guests), I can use DirectSound and MME for output,
and sound has no interrupts, of both computers. If I run it in 32-bit
Vista guest, only Kernel Streaming in Foobar2000 allows to achieve
uninterrupted sound. MME usage causes some breaks, and DirectSound
usage causes many frequent breaks.

My virtual device driver (Virtual Audio Cable) works fine in
Win2000/XP/2003 guests, almost fine in 64-bit Vista guest, and shows
many buffer underruns (no available mappings, I use WavePci)
in 32-bit Vista guest.

Additionally, I measured boot, logon and shutdown times for 32 and
64-bit Vista guests:

Desktop (boot / logon / shutdown), sec:

32-bit Vista - 130 / 16 / 19
64-bit Vista - 104 / 6 / 9


32-bit Vista - 62 / 5 / 25
64-bit Vista - 38 / 3 / 10

Host systems are 32-bit XP SP2/SP3 (desktop) and 32-bit XP SP2/SP3,
64-bit XP SP1, 32-bit Vista SP1 (notebook). No difference. In 64-bit
host system, all VMs perform slightly faster but 32-bit Vista performs
MUCH slower than every other system.

Both 32-bit and 64-bit Vista VMs have 600 MB of memory, virtual disks are 
resided physically
near to each other, both defragmented. Tried to increase VM memory up
to 2048 MB, but no effect.

I tried monitor_control.vt32=true and monitor.virtual_mmu=hardware but there 
was no effect.

Question 1: Does anybody know why 32-bit Vista performs so slow in VM, 
especially in
audio stack activity (DirectSound/MME), in comparison to

Question 2: Does anybody know what hardware (CPU/chipset/HDD) I need to get 
32-bit Vista
guest performance noticeably faster so it will work with audio streams without



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