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Re: upreempt_pri

On 01/10/2012 03:30 AM, YAMAMOTO Takashi wrote:
> hi,
>> Hi,
>> I would like to change upreempt_pri to default to 0 as this makes
>>  wakeups where the interrupted cpu schedules a thread on another
>> cpu behave like as if it where scheduled on the interrupted cpu.
>> For the case that  the to be scheduled on cpu is the interrupted
>> one, the behavior is like having upreempt_pri set to 0, as
>> rescheduling happens on return too usermode while in the cross
>> cpu case this might be delayed until the next timer interrupt.
>> This change makes some sluggishness regarding X to go a way. 
>> (Solaris defaults to 0 here as well, I think the only reason to
>> set it higher is on very big SMP machines where throughput is
>> more important then latency)
>> Lars
> i'm not sure how it can make much differences given that l_kpribase
> is normally PRI_KERNEL.

isn't eprio in that case a user space priority if the thread was
preempted during user space execution?

> can you explain a little more? or, even better, can you try to
> create a smaller test program to demonstrate the sluggishness?

The rational behind this is that the highest priority thread should
run which is not always the case if user space preemption had happened.
On my machine the behavior is quite obvious with compiles running in
the background and moving windows in X.



Mystische Erklärungen:
Die mystischen Erklärungen gelten für tief;
die Wahrheit ist, dass sie noch nicht einmal oberflächlich sind.

   -- Friedrich Nietzsche
   [ Die Fröhliche Wissenschaft Buch 3, 126 ]

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