Messages in this thread | | | Subject | Re: [Lse-tech] more on scheduler benchmarks | From | "Hubertus Franke" <> | Date | Mon, 22 Jan 2001 14:27:03 -0500 |
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Mike,
Deactivating that optimization is a good idea. What we are interested in is what the general latency of the scheduler code is. This should help to determine that.
The only problem I have with sched_yield like benchmarks is that it creates artificial lock contention as we basically spent most of the time other then context switching + syscall under the scheduler lock. This we won't see in real apps, that's why I think the chatroom numbers are probably better indicators.
Hubertus Franke Enterprise Linux Group (Mgr), Linux Technology Center (Member Scalability) , OS-PIC (Chair) email: frankeh@us.ibm.com (w) 914-945-2003 (fax) 914-945-4425 TL: 862-2003
Mike Kravetz <mkravetz@sequent.com>@lists.sourceforge.net on 01/22/2001 01:17:38 PM
Sent by: lse-tech-admin@lists.sourceforge.net
To: lse-tech@lists.sourceforge.net cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu> Subject: [Lse-tech] more on scheduler benchmarks
Last week while discussing scheduler benchmarks, Bill Hartner made a comment something like the following "the benchmark may not even be invoking the scheduler as you expect". This comment did not fully sink in until this weekend when I started thinking about changes made to sched_yield() in 2.4.0. (I'm cc'ing Ingo Molnar because I think he was involved in the changes). If you haven't taken a look at sys_sched_yield() in 2.4.0, I suggest that you do that now.
A result of new optimizations made to sys_sched_yield() is that calling sched_yield() does not result in a 'reschedule' if there are no tasks waiting for CPU resources. Therefore, I would claim that running 'scheduler benchmarks' which loop doing sched_yield() seem to have little meaning/value for runs where the number of looping tasks is less than then number of CPUs in the system. Is that an accurate statement?
If the above is accurate, then I am wondering what would be a good scheduler benchmark for these low task count situations. I could undo the optimizations in sys_sched_yield() (for testing purposes only!), and run the existing benchmarks. Can anyone suggest a better solution?
Thanks, -- Mike Kravetz mkravetz@sequent.com IBM Linux Technology Center 15450 SW Koll Parkway Beaverton, OR 97006-6063 (503)578-3494
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