Messages in this thread | | | Date | Mon, 29 Dec 2003 18:02:37 +1100 | From | Nick Piggin <> | Subject | Re: [PATCH] 2.6.0 batch scheduling, HT aware |
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Pavel Machek wrote:
>Hi! > > >>>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. >> > >Well, gigaherz is not the *only* important thing. > >On 2x1GHz, 2GB/sec RAM bandwidth, fastest a single threaded task can >run is 1GHz, 2GB/sec. If you run two of them, it is 1GHz, >*1*GB/sec. So you still have effect similar to hyperthreading. And >yes, it can be measured. >
Hi Pavel, Sure this might be a real problem sometimes, but I don't see the CPU scheduler ever handling it unless we want to add a few kitchen sinks to its nice lean code as well.
If the need really arises, then probably a userspace daemon could do it.
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