> Date: Thu, 12 Aug 2010 13:53:51 -0400 > From: Jeff Angielski <j...@theptrgroup.com> > To: linuxppc-dev@lists.ozlabs.org > Subject: Re: Query regarding 2.6.335 RT[Ingo's] and Non-RT performance > Message-ID: <4c64352f.4090...@theptrgroup.com> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > On 08/11/2010 06:18 PM, Manikandan Ramachandran wrote: > > Hello All, > > I created a very simple program which has higher priority than > > normal tasks and runs a tight loop. Under same test environment I ran > > this program on both non-rt and rt 2.6.33.5 kernel. To my suprise I see > > that performance of non-RT kernel is better than RT. non-RT kernel took > > 3 sec and 366156 usec while RT kernel took about 3 sec and 418011 > > usec.Can someone please explain why the performance of non-rt kernel is > > better than rt kernel? From the face of the test result, I feel RT has > > more overhead,Is there any configuration that I could do to bring down > > the overhead? > > Your "surprise" is due to your definition of "performance". > > The purpose of the -rt kernels is to reduce the kernel latency. This is > important for servicing hardware. Normal users find the -rt useful for > audio/video applications. Engineering and scientific users find the -rt > beneficially for servicing hardware like sensors or control systems. > > If you are just trying to run calculations as fast as you can in user > space, you'd be better off using the non-rt variants. > > > -- > Jeff Angielski > The PTR Group > www.theptrgroup.com > > > Thanks for your response. > > On one hand I hear that RT-kernel is meant for reducing kernel latency on > other hand I see that there is RT-kernel overhead. So what really RT-kernel > brings to system performance? > > Actually I see that latency for higher priority is more or less same for > non-rt system. > > One more thing, since irqs being threaded in RT, and with CFS scheduler in > 2.6.33, wouldn't we bring down system performance as CFS is O(log(n)) in > nature? > -- > Thanks, > Manik >
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