Re: status of Preemptible Kernel 2.6.7
From: Timothy Miller
Date: Wed Jun 23 2004 - 14:12:30 EST
Robert Love wrote:
On Wed, 2004-06-23 at 13:57 -0400, Timothy Miller wrote:
I vaguely recall someone recently talking about eliminating preempt by
improving low-latency. See, if everything were ideal, we wouldn't need
preempt, because all drivers would yield the CPU at appropriate times.
If everything held locks for only sane periods of time, we would not
need gross explicit yielding all over the place.
To answer Marcus's question: go for it and use it.
I wasn't talking about locks. I was talking about kernel functions
taking long periods of time, cases where preempt has been useful to
reduce kernel latency.
Holding locks for extended periods is something else entirely.
I presume there are sane cases where a kernel function will need to
execute for a "long time", like when doing PIO disk access or COW, etc.
It would be good to have a way to limit the impact of those functions
in terms of user-perceived latency, just as preempt has done, but
without preempt.
At least, I thought that was the idea.
Now, the thing is, if you have explicit cooperative yields, then a slow
CPU might not yield often enough, and a fast CPU would yield too often.
Preempt has the advantage of using real time so that CPUs can
maximize throughput without affecting latency.
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