Re: [PATCH [RT] 00/14] RFC - adaptive real-time locks

[Andrew Morton]

On Thu, 21 Feb 2008 22:24:20 +0100 Ingo Molnar <mingo@xxxxxxx> wrote:

> regarding the concept: adaptive mutexes have been talked about in the 
> past, but their advantage is not at all clear, that's why we havent done 
> them. It's definitely not an unambigiously win-win concept.

When ext3 was converted from sleeping locks to spinlocks, dbench-on-numaq
throughput went up by a factor of ten.  I'd expect that what RT has done
was a truly awful change for lots of workloads on lots of machines.

Yeah, there's the dont-enable-it-if-you're-doing-that option, but that adds
the we-just-doubled-the-number-of-kernels-distros-need-to-ship problem.

Does -rt also make bit_spin_lock preemptible?  If not, I'd have thought the
change was of little benefit to ext3/jbd and it might as well go back to
spinning locks.

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