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SubjectRe: [PATCH [RT] 00/14] RFC - adaptive real-time locks
>>> On Thu, Feb 21, 2008 at  4:24 PM, in message <20080221212420.GA20953@elte.hu>,
Ingo Molnar <mingo@elte.hu> wrote:

> hm. Why is the ticket spinlock patch included in this patchset? It just
> skews your performance results unnecessarily. Ticket spinlocks are
> independent conceptually, they are already upstream in 2.6.25-rc2 and
> -rt will have them automatically once we rebase to .25.

Sorry if it was ambiguous. I included them because we found the patch series without them can cause spikes due to the newly introduced pressure on the (raw_spinlock_t)lock->wait_lock. You can run the adaptive-spin patches without them just fine (in fact, in many cases things run faster without them....dbench *thrives* on chaos). But you may also measure a cyclic-test spike if you do so. So I included them to present a "complete package without spikes". I tried to explain that detail in the prologue, but most people probably fell asleep before they got to the end ;)
>
> and if we take the ticket spinlock patch out of your series, the the
> size of the patchset shrinks in half and touches only 200-300 lines of
> code ;-) Considering the total size of the -rt patchset:
>
> 652 files changed, 23830 insertions(+), 4636 deletions(-)
>
> we can regard it a routine optimization ;-)

Its not the size of your LOC, but what you do with it :)

>
> 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.
>
> So lets get some real marketing-free benchmarking done, and we are not
> just interested in the workloads where a bit of polling on contended
> locks helps, but we are also interested in workloads where the polling
> hurts ... And lets please do the comparisons without the ticket spinlock
> patch ...

I'm open to suggestion, and this was just a sample of the testing we have done. We have thrown plenty of workloads at this patch series far beyond the slides I prepared in that URL, and they all seem to indicate a net positive improvement so far. Some of those results I cannot share due to NDA, and some I didnt share simply because I never formally collected the data like I did for these tests. If there is something you would like to see, please let me know and I will arrange for it to be executed if at all possible.

Regards,
-Greg



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