Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.43-00

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux