Messages in this thread | | | From | Con Kolivas <> | Subject | Re: [PATCH] 2.6.0 batch scheduling, HT aware | Date | Sat, 27 Dec 2003 10:42:55 +1100 |
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On Sat, 27 Dec 2003 09:56, Pavel Machek wrote: > Hi! > > > I've done a resync and update of my batch scheduling that is also > > hyper-thread aware. > > > > What is batch scheduling? Specifying a task as batch allows it to only > > use cpu time if there is idle time available, rather than having a > > proportion of the cpu time based on niceness. > > > > Why do I need hyper-thread aware batch scheduling? > > > > If you have a hyperthread (P4HT) processor and run it as two logical cpus > > you can have a very low priority task running that can consume 50% of > > your physical cpu's capacity no matter how high priority tasks you are > > running. For example if you use the distributed computing client > > setiathome you will be effectively be running at half your cpu's speed > > even if you run setiathome at nice 20. Batch scheduling for normal cpus > > allows only idle time to be used for batch tasks, and for HT cpus only > > allows idle time when both logical cpus are idle. > > BTW this is going to be an issue even on normal (non-HT) > systems. Imagine memory-bound scientific task on CPU0 and nice -20 > memory-bound seti&home at CPU1. Even without hyperthreading, your > scientific task is going to run at 50% of speed and seti&home is going > to get second half. Oops. > > Something similar can happen with disk, but we are moving out of > cpu-scheduler arena with that. > > [I do not have SMP nearby to demonstrate it, anybody wanting to > benchmark a bit?]
This is definitely the case but there is one huge difference. If you have 2x1Ghz non HT processors then the fastest a single threaded task can run is at 1Ghz. If you have 1x2Ghz HT processor the fastest a single threaded task can run is 2Ghz.
Con
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