[wdmaudiodev] Slow string debug output from multiprocessor systems
- From: Eugene Muzychenko <eugene@xxxxxxxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Mon, 7 Nov 2011 22:40:04 +0700
Hello!
Using VM kernel debugging (VMware/VBox) with WinDbg and VirtualKD
(virtualkd.sysprogs.org), I noticed that string debug output
(DbgPrint/OutputDebugString) from multiprocessor Windows is VERY slow
(no more than a hundred of 64-character messages per second). If I
changed Windows mode to uniprocessor (for example, by adding ONECPU
option), string output speed is dramatically increased (thousands of
messages per second).
I thought that is VirtualKD problem but today I ran a test on hardware
XP and Win7 targets connected via 1394 and got exactly the same results. A very
simple program that executes OutputDebugString with a static
64-character string in a single thread, demonstrated 220 microseconds
per line in uniprocessor mode and 12 milliseconds per line in default
two-processor mode (target CPU was Core 2 Duo T8300).
I'm afraid Windows uses a kind of all-CPU synchronization method for
string output. Does somebody know the details? And is there a way to
speed-up string output from multiprocessor systems?
With 2k/XP targets, I use DebugView from Sysinternals with "Pass
through" option disabled. It allows to intercept all string output in
the local system. But in Vista/Win7, DebugView uses a different
interception algorithm that does not allow to prevent strings from
sending to a remote debugger.
Regards,
Eugene
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