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 -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
