Project Home
Project Home		 Documents
Documents		 Wiki
Wiki		 Discussion Forums
Discussions		 Project Information
Project Info
QNX Operating System/Discussion/OSTech/Low cost, fast way to get thread status.sutime value in /proc/<proc id>, alternative approach?/List of Posts
Forum Topic - Low cost, fast way to get thread status.sutime value in /proc/<proc id>, alternative approach?: (3 Items)
   
Update
David Beberman(deleted)
04/01/2015 11:29 PM
post113670
Low cost, fast way to get thread status.sutime value in /proc/<proc id>, alternative approach?   
Hi,
I'm looking for a way to get the accurate actual execution time of individual threads in a process.
I'm aware of opening the /proc/<proc id> and then using devctl() call with a pthread_t value to get
the status of the thread, which includes the sutime value.

This is a kernel call, which by definition includes a CPU syscall gate, and a call to the QNX scheduler.
For my uses, this is too heavy weight.
Is there any way to read this value with reduced overhead?
Ideally, something that avoids the callgate and the scheduler call altogether.

I have not seen anything like this.  I did see a discussion from about 7 years ago about trying to
provide some sort of large bulk transfer API.  An abortive discussion about memory mapping read-only
kernel structures.  Is there anything else?

Thanks,
David Beberman
Brian Stecher
04/02/2015 8:18 AM
post113671
RE: Low cost, fast way to get thread status.sutime value in /proc/<proc id>, alternative approach?   
A devctl() is actually a message pass to the process manager, which involves multiple kernel calls. There is
a cheaper mechanism, but it still involves one kernel call (actually two, but the first only has to be done one time per
 thread).

   id = ClockId(<pid>, <tid>);

   for( ;; ) {
      ...
      ClockTime(id, NULL, &running_time);
      ...
   }

that's as cheap as you can get it.
________________________________________
From: David Beberman [community-noreply@qnx.com]
Sent: April-01-15 11:29 PM
To: ostech-core_os
Subject: Low cost, fast way to get thread status.sutime value in /proc/<proc id>, alternative approach?

Hi,
I'm looking for a way to get the accurate actual execution time of individual threads in a process.
I'm aware of opening the /proc/<proc id> and then using devctl() call with a pthread_t value to get
the status of the thread, which includes the sutime value.

This is a kernel call, which by definition includes a CPU syscall gate, and a call to the QNX scheduler.
For my uses, this is too heavy weight.
Is there any way to read this value with reduced overhead?
Ideally, something that avoids the callgate and the scheduler call altogether.

I have not seen anything like this.  I did see a discussion from about 7 years ago about trying to
provide some sort of large bulk transfer API.  An abortive discussion about memory mapping read-only
kernel structures.  Is there anything else?

Thanks,
David Beberman



_______________________________________________

OSTech
http://community.qnx.com/sf/go/post113670
To cancel your subscription to this discussion, please e-mail ostech-core_os-unsubscribe@community.qnx.com
David Beberman(deleted)
04/25/2015 3:59 PM
post113746
Re: RE: Low cost, fast way to get thread status.sutime value in /proc/<proc id>, alternative approach?   
Thanks.
We implemented with devctl().  If this saves a few more cycles, will advise that we shift to it.
Just checked the doc on it.  Thanks for the direction.

> A devctl() is actually a message pass to the process manager, which involves 
> multiple kernel calls. There is
> a cheaper mechanism, but it still involves one kernel call (actually two, but 
> the first only has to be done one time per thread).
> 
>    id = ClockId(<pid>, <tid>);
> 
>    for( ;; ) {
>       ...
>       ClockTime(id, NULL, &running_time);
>       ...
>    }
> 
> that's as cheap as you can get it.
> ________________________________________
> From: David Beberman [community-noreply@qnx.com]
> Sent: April-01-15 11:29 PM
> To: ostech-core_os
> Subject: Low cost, fast way to get thread status.sutime value in /proc/<proc id>, 
> alternative approach?
> 
> Hi,
> I'm looking for a way to get the accurate actual execution time of individual 
> threads in a process.
> I'm aware of opening the /proc/<proc id> and then using devctl() call with a pthread_t 
> value to get
> the status of the thread, which includes the sutime value.
> 
> This is a kernel call, which by definition includes a CPU syscall gate, and a 
> call to the QNX scheduler.
> For my uses, this is too heavy weight.
> Is there any way to read this value with reduced overhead?
> Ideally, something that avoids the callgate and the scheduler call altogether.
> 
> I have not seen anything like this.  I did see a discussion from about 7 years
>  ago about trying to
> provide some sort of large bulk transfer API.  An abortive discussion about 
> memory mapping read-only
> kernel structures.  Is there anything else?
> 
> Thanks,
> David Beberman
> 
> 
> 
> _______________________________________________
> 
> OSTech
> http://community.qnx.com/sf/go/post113670
> To cancel your subscription to this discussion, please e-mail ostech-core_os-
> unsubscribe@community.qnx.co

Return


  A subsidiary of BlackBerry             All content ©2004-2013, QNX Software Systems