Re: [PATCH RFC 1/2] qrwlock: A queue read/write lock implementation

[Waiman Long]

On 07/22/2013 06:34 AM, Ingo Molnar wrote:
> * Waiman Long<waiman.long@xxxxxx>  wrote:
>
> > I had run some performance tests using the fserver and new_fserver
> > benchmarks (on ext4 filesystems) of the AIM7 test suite on a 80-core
> > DL980 with HT on. The following kernels were used:
> >
> > 1. Modified 3.10.1 kernel with mb_cache_spinlock in fs/mbcache.c
> >     replaced by a rwlock
> > 2. Modified 3.10.1 kernel + modified __read_lock_failed code as suggested
> >     by Ingo
> > 3. Modified 3.10.1 kernel + queue read/write lock
> > 4. Modified 3.10.1 kernel + queue read/write lock in classic read/write
> >     lock behavior
> >
> > The last one is with the read lock stealing flag set in the qrwlock
> > structure to give priority to readers and behave more like the classic
> > read/write lock with less fairness.
> >
> > The following table shows the averaged results in the 200-1000
> > user ranges:
> >
> > +-----------------+--------+--------+--------+--------+
> > |  Kernel         |    1   |    2   |    3   |   4    |
> > +-----------------+--------+--------+--------+--------+
> > | fserver JPM     | 245598 | 274457 | 403348 | 411941 |
> > | % change from 1 |   0%   | +11.8% | +64.2% | +67.7% |
> > +-----------------+--------+--------+--------+--------+
> > | new-fserver JPM | 231549 | 269807 | 399093 | 399418 |
> > | % change from 1 |   0%   | +16.5% | +72.4% | +72.5% |
> > +-----------------+--------+--------+--------+--------+
> So it's not just herding that is a problem.
>
> I'm wondering, how sensitive is this particular benchmark to fairness?
> I.e. do the 200-1000 simulated users each perform the same number of ops,
> so that any smearing of execution time via unfairness gets amplified?
>
> I.e. does steady-state throughput go up by 60%+ too with your changes?

For this particular benchmark, there are interplay of different locks 
that determine the overall performance of the system. Yes, I got steady 
state performance gain of 60%+ with the qrwlock change with the modified 
mbcache.c. Without the modified mbcache.c file, the performance gain 
drop to 20-30%. I am still trying to find out more about the performance 
variations in different situations.

Regards,
Longman
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