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

[Sedat Dilek]

On Fri, Aug 30, 2013 at 11:58 AM, Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
> 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
>

[ Sorry for being off-topic ]

Hey Ingo,

can you help, please?

I installed so far all missing -dev packages...

$ sudo apt-get install libelf-dev libdw-dev libunwind7-dev libslang2-dev

...and then want a perf-only build...

[ See tools/Makefile ]

$ LANG=C LC_ALL=C make -C tools/ perf_install 2>&1 | tee ../perf_install-log.txt

This ends up like this:
...
make[2]: Entering directory
`/home/wearefam/src/linux-kernel/linux/tools/lib/traceevent'
make[2]: Leaving directory
`/home/wearefam/src/linux-kernel/linux/tools/lib/traceevent'
    LINK perf
gcc: error: /home/wearefam/src/linux-kernel/linux/tools/lib/lk/liblk.a:
No such file or directory
make[1]: *** [perf] Error 1
make[1]: Leaving directory `/home/wearefam/src/linux-kernel/linux/tools/perf'
make: *** [perf_install] Error 2

$ LANG=C LC_ALL=C ll tools/lib/lk/
total 20
drwxr-xr-x 2 wearefam wearefam 4096 Aug 30 12:11 ./
drwxr-xr-x 4 wearefam wearefam 4096 Jul 11 19:42 ../
-rw-r--r-- 1 wearefam wearefam 1430 Aug 30 09:56 Makefile
-rw-r--r-- 1 wearefam wearefam 2144 Jul 11 19:42 debugfs.c
-rw-r--r-- 1 wearefam wearefam  619 Jul 11 19:42 debugfs.h

Why is liblk not built?

- Sedat -

P.S.: To clean perf build, run...

$ LANG=C LC_ALL=C make -C tools/ perf_clean
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