Re: [dpdk-dev] [PATCH v1 0/3] MCS queued lock implementation

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

On Wed, Jun 5, 2019 at 6:00 PM Phil Yang <phil.yang@arm.com<mailto:phil.yang@arm.com>> wrote:
This patch set added MCS lock library and its unit test.

The MCS lock (proposed by JOHN M. MELLOR-CRUMMEY and MICHAEL L. SCOTT) provides
scalability by spinning on a CPU/thread local variable which avoids expensive
cache bouncings. It provides fairness by maintaining a list of acquirers and
passing the lock to each CPU/thread in the order they acquired the lock.

References:
1. http://web.mit.edu/6.173/www/currentsemester/readings/R06-scalable-synchronization-1991.pdf
2. https://lwn.net/Articles/590243/

Mirco-benchmarking result:
------------------------------------------------------------------------------------------------
MCS lock                      | spinlock                       | ticket lock
------------------------------+--------------------------------+--------------------------------
Test with lock on 13 cores... |  Test with lock on 14 cores... |  Test with lock on 14 cores...
Core [15] Cost Time = 22426 us|  Core [14] Cost Time = 47974 us|  Core [14] cost time = 66761 us
Core [16] Cost Time = 22382 us|  Core [15] Cost Time = 46979 us|  Core [15] cost time = 66766 us
Core [17] Cost Time = 22294 us|  Core [16] Cost Time = 46044 us|  Core [16] cost time = 66761 us
Core [18] Cost Time = 22412 us|  Core [17] Cost Time = 28793 us|  Core [17] cost time = 66767 us
Core [19] Cost Time = 22407 us|  Core [18] Cost Time = 48349 us|  Core [18] cost time = 66758 us
Core [20] Cost Time = 22436 us|  Core [19] Cost Time = 19381 us|  Core [19] cost time = 66766 us
Core [21] Cost Time = 22414 us|  Core [20] Cost Time = 47914 us|  Core [20] cost time = 66763 us
Core [22] Cost Time = 22405 us|  Core [21] Cost Time = 48333 us|  Core [21] cost time = 66766 us
Core [23] Cost Time = 22435 us|  Core [22] Cost Time = 38900 us|  Core [22] cost time = 66749 us
Core [24] Cost Time = 22401 us|  Core [23] Cost Time = 45374 us|  Core [23] cost time = 66765 us
Core [25] Cost Time = 22408 us|  Core [24] Cost Time = 16121 us|  Core [24] cost time = 66762 us
Core [26] Cost Time = 22380 us|  Core [25] Cost Time = 42731 us|  Core [25] cost time = 66768 us
Core [27] Cost Time = 22395 us|  Core [26] Cost Time = 29439 us|  Core [26] cost time = 66768 us
                              |  Core [27] Cost Time = 38071 us|  Core [27] cost time = 66767 us
------------------------------+--------------------------------+--------------------------------
Total Cost Time = 291195 us   |  Total Cost Time = 544403 us   |  Total cost time = 934687 us
------------------------------------------------------------------------------------------------

Had a quick look, interesting.

Quick comments:
- your numbers are for 13 cores, while the other are for 14, what is the reason?
- do we need per architecture header? all I can see is generic code, we might as well directly put rte_mcslock.h in the common/include directory.
- could we replace the current spinlock with this approach? is this more expensive than spinlock on lowly contended locks? is there a reason we want to keep all these approaches? we could have now 3 lock implementations.
- do we need to write the authors names in full capitalized version? it seems like you are shouting :-)
[Honnappa] IMO, writing full names is a cultural thing? I do not see any harm. But, I do think, we do not need to capitalize everything.


--
David Marchand
[Honnappa] This mail is appearing as HTML, would be good to change to text mode. It is much easier to add inline comments.