Messages in this thread | | | Date | Tue, 05 Apr 2005 17:18:17 +0200 | From | Mike Galbraith <> | Subject | Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.43-00 |
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At 01:57 AM 4/5/2005 -0600, Zwane Mwaikambo wrote: >On Tue, 5 Apr 2005, Esben Nielsen wrote: > > > > I'm sure a lot of the yield() users could be converted to > > > schedule_timeout(), some of the users i saw were for low memory > conditions > > > where we want other tasks to make progress and complete so that we a bit > > > more free memory. > > > > > > > Easy, but damn ugly. Completions are the right answer. The memory system > > needs a queue system where tasks can sleep (with a timeout) until the > > right amount of memory is available instead of half busy-looping. > >I agree entirely, that would definitely be a better way to go eventually.
I wouldn't bet on it. There used to be a queue - minus the timeout. Throughput improved markedly with it's removal.
That said, yield()s in the kernel can be quite evil. I once instrumented semaphores, and under hefty load, frequently found tasks waiting for a semaphore held by someone in the expired array. When you've got a busy cpu, that wait can be _extremely_ painful. The yield()s in mm/*.c are long gone (thank god), but after a quick grep/peek, I can imagine the one in free_more_memory() causing some throughput grief in a cpu intense environment, and the one in __wait_on_freeing_inode() would punt you into the dungeon while you're holding the inode lock... that looks like it could be pretty unpleasant.
-Mike
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