[linux-audio-user] Kernel 2.6.x latency

Stephen Hassard steve at hassard.net
Thu Mar 11 16:24:08 EST 2004


Hi,

Has anyone tried the different IO schedulers with 2.6? I've seen some 
systems that feel much more responsive with the non-default Deadline 
scheduler than the default anticipatory scheduler .. I haven't done any 
audio specific latency tests though.

later,
Steve

Jack O'Quin wrote:
> James Stone <stone1 at btinternet.com> writes:
> 
> 
>>On Thu, Mar 11, 2004 at 06:21:15PM +0100, Frank Barknecht wrote:
> 
> 
>>>Another thing to check would be your X server's nice value. This used
>>>to be "-10" in older Debians, but should not be set at all with 2.6. 
> 
> 
>>How disappointing.. I just tried this, and it didn't help.. I was almost
>>sure this was going to work. I am still getting many more xruns than
>>with the low latency 2.4.x kernels though at least I am not getting
>>xruns on opening and closing windows!
>>
>>However, on doing a top in 2.6.x I noticed that quite a few processes
>>are running with a nice of -10 (something called "event" among
>>others..). This does not appear to be the case in 2.4.x.. perhaps this
>>could be the source of the trouble.. not really sure how to fix it
>>though.
> 
> 
> This makes me wonder if there is a bug in the scheduler.  IIUC, a
> realtime thread is *supposed* to have higher priority than any
> non-SCHED_FIFO thread, regardless of "nice" value.  
> 
> If we can nail down a case where this is definitely happening, someone
> should report it to Andrew Morton.
> 
> 
>>I will have to stick with 2.4.25 for the time being by the looks of
>>things.
> 
> 
> You can almost certainly get better low-latency results that way, at
> least for the moment.  I hope that over time 2.6.x will become just as
> good.


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