[Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Marc-Andre Laverdiere-Papineau]

Hello all!

I'm working on an application where every Bluetooth device is trying to
scan for every other one around, and check if it runs my custom service.
At the same time, said service is running in another thread, waiting to be
connected to.

I am using Rococo with Bluez. Kernel RH2.4.28, latest version of BlueZ.
Belkin FT003 dongles.

When I have one computer having the service opened+performing the scan,
while the other just performs the scan, things go fine. The scans are
timely and I can send a message.

However, then I have both computers running the service+the service scan,
things slow down to a crawl. Actually, it depends on its mood.
 It can take a full minute to have a device scan and a service scan
completing, or less than 20 seconds! Sometimes, computer a  will be able
to detect computer b, while B still shows no sign of life.

On top of things, if I manage to get it to send a message to its peer, the
peer will get an Exception :( I was able to fix this by preventing the
application from doing a service scan at the moment it would send, but
that didn't fix the weird behaviour on service discovery. This hackaround
is not sturdy and I don't like it as a general thing.

Has such thing ever happened to any of you? What can I do to fix it?

It looks like Bluetooth won't let me open a connection while doing a
service scan. Is there limitations on what can be running simultaneously?
It looks like service scan + opening connections is no good. Should I
know other ones like that?

Thanks

MA



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Re: [Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Marcel Holtmann]

Hi Marc-Andre,

> I'm working on an application where every Bluetooth device is trying to
> scan for every other one around, and check if it runs my custom service.
> At the same time, said service is running in another thread, waiting to be
> connected to.
> 
> I am using Rococo with Bluez. Kernel RH2.4.28, latest version of BlueZ.
> Belkin FT003 dongles.
> 
> When I have one computer having the service opened+performing the scan,
> while the other just performs the scan, things go fine. The scans are
> timely and I can send a message.
> 
> However, then I have both computers running the service+the service scan,
> things slow down to a crawl. Actually, it depends on its mood.
>  It can take a full minute to have a device scan and a service scan
> completing, or less than 20 seconds! Sometimes, computer a  will be able
> to detect computer b, while B still shows no sign of life.
> 
> On top of things, if I manage to get it to send a message to its peer, the
> peer will get an Exception :( I was able to fix this by preventing the
> application from doing a service scan at the moment it would send, but
> that didn't fix the weird behaviour on service discovery. This hackaround
> is not sturdy and I don't like it as a general thing.
> 
> Has such thing ever happened to any of you? What can I do to fix it?
> 
> It looks like Bluetooth won't let me open a connection while doing a
> service scan. Is there limitations on what can be running simultaneously?
> It looks like service scan + opening connections is no good. Should I
> know other ones like that?

please speak in terms of the Bluetooth specification. What are you
doing? Inquiry, page, service discovery or what?

Regards

Marcel




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Re: [Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Marcel Holtmann]

Hi Marc-Andre,

> Each system is perpetually running the following:
> 1- Device discovery (on a constant basis)
> 2- Service discovery on detected devices (for one particular service)
> (I made a quick hack not to scan already scanned devices. So this is not
> 'perpetually running' per se)
> 3- A L2CAP service
> 
> and they might try to open a connection to send data to the other one, etc.
> I'm using default BlueZ settings, so I do not know if there are options for
> each
> of those that might change anything.

so it is possible that you run an inquiry while you page another device.
Actually I don't know if this is supported by any Bluetooth chips on the
market. And you run an inquiry while you have an ACL link opened. This
works with most devices that supports scatternet, but is not one of the
best ideas and can decrease your performance. What does "hciconfig -a"
say about your devices?

Regards

Marcel




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Re: [Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Marc-Andre Laverdiere-Papineau]

Thanks Marcel for the help!

I'm not following all the terminology, since
I'm working with Java. I was wondering what you would suggest that would
be better for performance.

This project is about ad-hoc networking and so the devices need to be
constantly looking out for others that can be part of the network. The
design wasn't built thinking that performance would be so hit. Do you have
any idea why those two scenarios are different?

Scenario 1:
Device A: Device Discovery, Service Discovery, connects to Device B and
sends data
Device B: Device Discovery, Service Discovery, L2CAP service
This works super well. In this context the Service Discovery for Device B
never finds anything. I don't know if that makes a difference or not.

Scenario 2:
Device A: Device Discovery, Service Discovery, L2CAP service, connects to
Device B and sends data
Device B: Device Discovery, Service Discovery, L2CAP service
This makes me wish I never got in this project :(

On Mon, 16 Feb 2004, Marcel Holtmann wrote:
<snip>
> so it is possible that you run an inquiry while you page another device.
Actually, in the current situation, we have only 2 'devices', so they
boringly scan each other and that's it.

Hciconfig shows a few options for page scan (device discovery?) and
inquiry scan (service discovery?). Should I consider tweaking those?
> Actually I don't know if this is supported by any Bluetooth chips on the
> market. And you run an inquiry while you have an ACL link opened. This
> works with most devices that supports scatternet, but is not one of the
> best ideas and can decrease your performance. What does "hciconfig -a"
> say about your devices?
<snip>
It says:
# hciconfig hci0 up
# sdpd
# hciconfig -a
hci0:   Type: USB
        BD Address: 00:0A:3A:50:9C:DA ACL MTU: 192:8  SCO MTU: 64:8
        UP RUNNING PSCAN ISCAN
        RX bytes:69 acl:0 sco:0 events:8 errors:0
        TX bytes:27 acl:0 sco:0 commands:7 errors:0
        Features: 0xff 0xff 0x0b 0x00 0x00 0x00 0x00 0x00
        Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3
        Link policy:
        Link mode: SLAVE ACCEPT
        Name: 'BlueZ (0)'
        Class: 0x000000
        Service Classes: Unspecified
        Device Class: Miscellaneous,
        HCI Ver: 1.1 (0x1) HCI Rev: 0x20d LMP Ver: 1.1 (0x1) LMP Subver:
0x20d
        Manufacturer: Cambridge Silicon Radio (10)

Re: [Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Marcel Holtmann]

Hi Marc-Andre,

> I'm not following all the terminology, since
> I'm working with Java. I was wondering what you would suggest that would
> be better for performance.

even if you work with Java you should follow the Bluetooth terminology,
because otherwise it can be possible that we speak of different things.

> Hciconfig shows a few options for page scan (device discovery?) and
> inquiry scan (service discovery?). Should I consider tweaking those?

No, you should read the Bluetooth specification and understand what
these two means, because you got them wrong.

Regards

Marcel




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Re: [Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Marcel Holtmann]

Hi Marc-Andre,

> Only the 1.2 spec is available for people not from member companies. I hope
> this
> version is OK.

this version is almost fine.

> I'll get the non-Java terminology right and I'll write an understandable report
> then. This is frustrating.

I don't think so.

	inquiry scan	-> device is visible
	page scan	-> device is connectable

	inquiry		-> search for other devices
	page		-> connect to another device

	SDP connection	-> service discovery (includes page)

Regards

Marcel




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Re: [Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Marc-André Laverdière]

I read the parts allowing me to have some kind of understanding of what's going
on :) Sorry for the delay, I had a hard deadline for a report.

Here's the situation in more Bluetooth-compliant terms:
Configuration:
Belkin FT0003 USB dongles
RedHat 9 with kernel 2.4.28, from RedHat
Running with latest released versions of BlueZ
Running Impronto 1.18
Running Java SDK 1.4.2.3


Bluetooth activity (all happening in Java):

Implicit: Inquiry Scan [device is set as GIAC]
Thread 1: Inquiry [aka Device Discovery] [runs perpetually, with some sleeping
between each iteration]
Thread 2: Page Scan [opening a service and waiting for clients with
acceptAndOpen()]
Thread 3: SDP Paging + Connection [Service Discovery] [does so when new devices
are found, could happen anytime. Sleeps most of the time]
Thread 4: Paging + Connection [L2CAP Connection as a slave] [happens at user's
input]

Computer A and Computer B are running this configuration
Planned Test:
Start program on both computers
Wait for both Computer A and Computer B to discover each other via Inquiry
User prompts Computer A to send a message to Computer B [creating a L2CAP
connection]
Computer B reads the message and closes the connection
Both shut down their services and exit cleanly

What happens:
Inconsistent behaviour. Service discovery can happen promptly on Computer A and
never finish on Computer B. Sometimes, service discovery completes around 20
seconds for both systems.
The L2CAP connection may not establish itself. Behaviour varies at every test's
run, but generally the results look like a deadlock has occured somewhere.
Very low Bluetooth performance compared to the speed of other configurations.

I hope this makes more sense. I have to read more about the Bluetooth spec, see
what I'm doing wrong Bluetooth-wise. Any sections particularly?

I'm also considering adjusting the settings of hciconfig as well as upgrading
to
kernel 2.6 (I was told that it generally had a huge improvement I/O-wise)

-- 
Marc-André Laverdière  (†)
Étudiant coop. en génie logiciel - Software Engineering Co-Op Student
Université Concordia - Concordia University
/"\
\ /    ASCII Ribbon Campaign
 X      against HTML e-mail 
/ \


Selon Marcel Holtmann <marcel@holtmann.org>:

> Hi Marc-Andre,
> 
> > Only the 1.2 spec is available for people not from member companies. I
> hope
> > this
> > version is OK.
> 
> this version is almost fine.
> 
> > I'll get the non-Java terminology right and I'll write an understandable
> report
> > then. This is frustrating.
> 
> I don't think so.
> 
> 	inquiry scan	-> device is visible
> 	page scan	-> device is connectable
> 
> 	inquiry		-> search for other devices
> 	page		-> connect to another device
> 
> 	SDP connection	-> service discovery (includes page)
> 
> Regards
> 
> Marcel
> 
> 

Re: [Bluez-users] Major slowdown when service discovery+opening a service happens on two systems trying to talk to each other

[Marcel Holtmann]

Hi Marc-Andre,

> Here's the situation in more Bluetooth-compliant terms:
> Configuration:
> Belkin FT0003 USB dongles
> RedHat 9 with kernel 2.4.28, from RedHat
> Running with latest released versions of BlueZ
> Running Impronto 1.18
> Running Java SDK 1.4.2.3

I can't tell you anything about the Java part, but the kernel version
that you are using don't exists ;)

> Bluetooth activity (all happening in Java):
> 
> Implicit: Inquiry Scan [device is set as GIAC]
> Thread 1: Inquiry [aka Device Discovery] [runs perpetually, with some sleeping
> between each iteration]
> Thread 2: Page Scan [opening a service and waiting for clients with
> acceptAndOpen()]
> Thread 3: SDP Paging + Connection [Service Discovery] [does so when new devices
> are found, could happen anytime. Sleeps most of the time]
> Thread 4: Paging + Connection [L2CAP Connection as a slave] [happens at user's
> input]
> 
> Computer A and Computer B are running this configuration
> Planned Test:
> Start program on both computers
> Wait for both Computer A and Computer B to discover each other via Inquiry
> User prompts Computer A to send a message to Computer B [creating a L2CAP
> connection]
> Computer B reads the message and closes the connection
> Both shut down their services and exit cleanly
> 
> What happens:
> Inconsistent behaviour. Service discovery can happen promptly on Computer A and
> never finish on Computer B. Sometimes, service discovery completes around 20
> seconds for both systems.
> The L2CAP connection may not establish itself. Behaviour varies at every test's
> run, but generally the results look like a deadlock has occured somewhere.
> Very low Bluetooth performance compared to the speed of other configurations.
> 
> I hope this makes more sense. I have to read more about the Bluetooth spec, see
> what I'm doing wrong Bluetooth-wise. Any sections particularly?

The problem that I see is that if device A runs an inquiry and device B
tries to page device A at the same time, this will fail. But this is a
topic for baseband experts and not for me. You can try to disable page
scan before you run an inquiry and re-enable it when your are finished.
Same goes for the inquiry scan.

Regards

Marcel




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