Low performance when using DriverWorks

NTDEV
1

Hi,

We have a project to rewritte code of our Win2K Drivers (written in C)for
PCI card to WDM Drivers using DriverWorks. A lot of code has been reused.
Only the front end is big different. The old one is in C and the new one
in C++ using DriverWorks template. The project is half completed.
Now we experienced a big drop of performance (4-5 times slower) in new
Drivers versus the old one.

To narrow down the problem. I’ve tried to compare the time it takes to
process a IOCTL in both drivers.

I used DriverWorks wizard to created a new sample WDM driver for PCI card
(do not have any of my old driver code)

I used the following sample code in an application to calculate the time
it takes to process one dummy IOCTL ( When receive the request from Kernel
driver, the Irp is completed right away without doing anything )

QueryPerformanceCounter(&Before);

DeviceIoControl( hDriver, IOCTL_DUMMY_TEST, … );

QueryPerformanceCounter(&After);

With a sample WDM Driver created by DriverWorks wizard,
It takes about ~0.210 ms

With a sample Win2k driver that I wrote using C
it takes only ~50 microssecond.

I have tried with both DriverWorks Debugbuild and Release build. The
Release build is a bit faster but it still in the odrder of 0.200ms

Anyone who used DriverWorks, have you timed the similar IOCTL and
experience the same thing as I did ?

I expect a little overhead with C++ but not that much.

The overhead is because of C++ or because of DriverWorks ??

Is there any thing I can do with DriverWorks to improve performance
(compiler setting etc …)

I posted the question to Compuware Tech support but do not yet receive
the answers. I want to hear from you, the experts and the ones have much
experience with C++ and DriverWorks.

Both drivers are build uisng MSVC 6.0 and Win2K DDK

Please help,

QUANG

2

If you have DriverStudio, you can turn on TrueTime, it should be able to
tell you where the bottlenecks are.

Alberto.

-----Original Message-----
From: Quang Vu [mailto:xxxxx@gage-applied.com]
Sent: Friday, May 23, 2003 10:39 AM
To: NT Developers Interest List
Subject: [ntdev] Low performance when using DriverWorks

Hi,

We have a project to rewritte code of our Win2K Drivers (written in C)for
PCI card to WDM Drivers using DriverWorks. A lot of code has been reused.
Only the front end is big different. The old one is in C and the new one
in C++ using DriverWorks template. The project is half completed.
Now we experienced a big drop of performance (4-5 times slower) in new
Drivers versus the old one.

To narrow down the problem. I’ve tried to compare the time it takes to
process a IOCTL in both drivers.

I used DriverWorks wizard to created a new sample WDM driver for PCI card
(do not have any of my old driver code)

I used the following sample code in an application to calculate the time
it takes to process one dummy IOCTL ( When receive the request from Kernel
driver, the Irp is completed right away without doing anything )

QueryPerformanceCounter(&Before);

DeviceIoControl( hDriver, IOCTL_DUMMY_TEST, … );

QueryPerformanceCounter(&After);

With a sample WDM Driver created by DriverWorks wizard,
It takes about ~0.210 ms

With a sample Win2k driver that I wrote using C
it takes only ~50 microssecond.

I have tried with both DriverWorks Debugbuild and Release build. The
Release build is a bit faster but it still in the odrder of 0.200ms

Anyone who used DriverWorks, have you timed the similar IOCTL and
experience the same thing as I did ?

I expect a little overhead with C++ but not that much.

The overhead is because of C++ or because of DriverWorks ??

Is there any thing I can do with DriverWorks to improve performance
(compiler setting etc …)

I posted the question to Compuware Tech support but do not yet receive
the answers. I want to hear from you, the experts and the ones have much
experience with C++ and DriverWorks.

Both drivers are build uisng MSVC 6.0 and Win2K DDK

Please help,

QUANG

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3

DriverWorks will not add that amount of overhead to your driver. C++ will
not add that amount of overhead to your driver.

I used my favorite performance analyzer TrueTime Driver Edition from
DriverStudio to examine 3 drivers (free builds):

  1. portio from the W2k DDK.
  2. portio from DriverWorks. This driver is basically the same driver as 1
    plus c++ and usage of a few DriverWorks utility classes. (c++ as a better
    c while maintaining DDK procedural driver design)
  3. portio from DriverWorks that does use the entire DriverWorks c++
    framework.

Each driver handles IOCTLs to preform port io and has a corresponding test
app.
After analyzing the drivers, the time to complete an IOCTL to read a byte
from a port where the following:

  1. Avg time to complete = 0.0025 ms
  2. Avg time to complete = 0.0026 ms
  3. Avg time to complete = 0.0022 ms (note that this ioctl handler has
    different, more efficient code)

The conclusion is that careful C++ coding adds neglible overhead (1/25) to
your driver. DriverWorks also adds minimal overhead to your driver.

The real performance issues have to do more with proper driver design to
minimize ring transitions and issues dealing with I/O bound nature of
drivers. Typical drivers are I/O bound and not CPU bound. So C++ doesn’t
hurt.

As for your problem, are you porting an NT kernel-mode legacy driver to
WDM? If that’s the case, the WDM driver must implement a plug and play
and power management state machine that impacts processing of IRP’s.
DriverWorks framework provides such state machines. A dummy IOCTL handler
will still process the plug and play and power managment state machine in
a WDM driver. This could explain some performance hit vs a legacy driver.

Please go thru Compuware Tech Support for more help on this issue.

I hope this helps.

Steve Smith
Compuware Corp.