Messages in this thread |  | | Subject | Re: 2.4.10-ac10-preempt lmbench output. | From | Robert Love <> | Date | 09 Oct 2001 22:37:56 -0400 |
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On Tue, 2001-10-09 at 22:30, Andrea Arcangeli wrote: > As said it's very very unlikely that preemption points can fix xmms > skips anyways, the worst scheduler latency is always of the order of the > msecs, to generate skips you need a latency of seconds. > > [...] > > There's nothing magic in the software, if you divide the cpu in 10 parts > and you give 1/10 of the cpu to xmms, but xmms needs 1/2 of the cpu to > play your .mp3 then there's nothing you can do to fix it but to tell > the scheduler to give more cpu to xmms (renicing to -20 gives more cpu
What if the CPU does divide its time into two 1/2 parts, and gives one each to xmms and dbench. Everything runs fine, since xmms needs 1/2 cpu to play without skips.
Now dbench (or any task) is in kernel space for too long. The CPU time xmms needs will of course still be given, but _too late_. Its just not a cpu resource problem, its a timing problem. xmms needs x units of CPU every y units of time. Just getting the x whenever is not enough.
With preempt-kernel patch, the long-lasting kernel space activity dbench is engaged in won't hog the CPU until it completes. When xmms is ready (time y arrives), the scheduler will yield the CPU.
Robert Love
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