Re: [PATCH v7 1/4] spinlock: A new lockref structure for locklessupdate of refcount

[Sedat Dilek]

On Fri, Aug 30, 2013 at 11:56 AM, Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
> On Fri, Aug 30, 2013 at 11:48 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>>
>> * Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
>>
>>> On Fri, Aug 30, 2013 at 9:55 AM, Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
>>> > On Fri, Aug 30, 2013 at 5:54 AM, Linus Torvalds
>>> > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>> >> On Thu, Aug 29, 2013 at 8:12 PM, Waiman Long <waiman.long@xxxxxx> wrote:
>>> >>> On 08/29/2013 07:42 PM, Linus Torvalds wrote:
>>> >>>>
>>> >>>> Waiman? Mind looking at this and testing? Linus
>>> >>>
>>> >>> Sure, I will try out the patch tomorrow morning and see how it works out for
>>> >>> my test case.
>>> >>
>>> >> Ok, thanks, please use this slightly updated patch attached here.
>>> >>
>>> >> It improves on the previous version in actually handling the
>>> >> "unlazy_walk()" case with native lockref handling, which means that
>>> >> one other not entirely odd case (symlink traversal) avoids the d_lock
>>> >> contention.
>>> >>
>>> >> It also refactored the __d_rcu_to_refcount() to be more readable, and
>>> >> adds a big comment about what the heck is going on. The old code was
>>> >> clever, but I suspect not very many people could possibly understand
>>> >> what it actually did. Plus it used nested spinlocks because it wanted
>>> >> to avoid checking the sequence count twice. Which is stupid, since
>>> >> nesting locks is how you get really bad contention, and the sequence
>>> >> count check is really cheap anyway. Plus the nesting *really* didn't
>>> >> work with the whole lockref model.
>>> >>
>>> >> With this, my stupid thread-lookup thing doesn't show any spinlock
>>> >> contention even for the "look up symlink" case.
>>> >>
>>> >> It also avoids the unnecessary aligned u64 for when we don't actually
>>> >> use cmpxchg at all.
>>> >>
>>> >> It's still one single patch, since I was working on lots of small
>>> >> cleanups. I think it's pretty close to done now (assuming your testing
>>> >> shows it performs fine - the powerpc numbers are promising, though),
>>> >> so I'll split it up into proper chunks rather than random commit
>>> >> points. But I'm done for today at least.
>>> >>
>>> >> NOTE NOTE NOTE! My test coverage really has been pretty pitiful. You
>>> >> may hit cases I didn't test. I think it should be *stable*, but maybe
>>> >> there's some other d_lock case that your tuned waiting hid, and that
>>> >> my "fastpath only for unlocked case" version ends up having problems
>>> >> with.
>>> >>
>>> >
>>> > Following this thread with half an eye... Was that "unsigned" stuff
>>> > fixed (someone pointed to it).
>>> > How do you call that test-patch (subject)?
>>> > I would like to test it on my SNB ultrabook with your test-case script.
>>> >
>>>
>>> Here on Ubuntu/precise v12.04.3 AMD64 I get these numbers for total loops:
>>>
>>> lockref:  w/o patch | w/ patch
>>> ======================
>>> Run #1: 2.688.094 | 2.643.004
>>> Run #2: 2.678.884 | 2.652.787
>>> Run #3: 2.686.450 | 2.650.142
>>> Run #4: 2.688.435 | 2.648.409
>>> Run #5: 2.693.770 | 2.651.514
>>>
>>> Average: 2687126,6 VS. 2649171,2 ( ???37955,4 )
>>
>> For precise stddev numbers you can run it like this:
>>
>>    perf stat --null --repeat 5 ./test
>>
>> and it will measure time only and print the stddev in percentage:
>>
>>  Performance counter stats for './test' (5 runs):
>>
>>        1.001008928 seconds time elapsed                                          ( +-  0.00% )
>>
>
> Hi Ingo,
>
> that sounds really good :-).
>
> AFAICS 'make deb-pkg' does not have support to build linux-tools
> Debian package where perf is included.
> Can I run an older version of perf or should I / have to try with the
> one shipped in Linux v3.11-rc7+ sources?
> How can I build perf standalone, out of my sources?
>

Hmm, I installed linux-tools-common (3.2.0-53.81).

$ perf stat --null --repeat 5 ./t_lockref_from-linus
perf_3.11.0-rc7 not found
You may need to install linux-tools-3.11.0-rc7

- Sedat -
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