Re: [bisected] pre-3.16 regression on open() scalability

[Dave Hansen <dave.hansen@intel.com>]

On 06/20/2014 09:30 AM, Paul E. McKenney wrote:
> On Fri, Jun 20, 2014 at 11:07:13AM -0500, Christoph Lameter wrote:
>> On Fri, 20 Jun 2014, Paul E. McKenney wrote:
>>
>>> And the fraction of the small systems that care that much about latency
>>> is also quite small.
>>
>> This also impacts general performance of course not only latency.
>>
>>> Of course, if you have performance results that show otherwise, please
>>> share them.
>>
>> We are discussing a performance problem right here.
> 
> We are engaging in a lot of -speculation- about an -alleged- performance
> problem.  I have posted a fix to the actual performance problem, but the
> guy reporting the original report of that problem has not yet reported
> the performance of the fix.  Which is fine, as I am getting ready to
> post an updated fix, and besides which he might well have higher-priority
> tasks requiring his attention.  But without that performance information,
> we are all just engaging in baseless speculation.

The patch helps, but does not get us back to where we were before:

Baseline: 3c8fb5044 with ac1bea85781e9004d reverted:
root@bigbox:~/will-it-scale# ./open1_processes -t 160 -s 30
...
average:57710064

3c8fb5044 with Paul's early version with the magic 7:
root@bigbox:~/will-it-scale# ./open1_processes -t 160 -s 30
...
average:48363361

It was down at 43M or 44M without the new patch.

full spew:

3c8fb50445833b93f69b6b703a29aae3523cad0c
with ac1bea85781e9004d reverted:
root@bigbox:~/will-it-scale# ./open1_processes -t 160 -s 30
warmup
min:366329 max:421686 total:63727790
min:358758 max:406036 total:62561168
min:298435 max:340355 total:51711000
min:343707 max:383812 total:59554601
min:310652 max:356571 total:54016014
min:337738 max:382557 total:59146223
measurement
min:317628 max:363489 total:55230696
min:341875 max:392621 total:59910047
min:331979 max:376582 total:58074347
min:342835 max:388481 total:59644247
min:327282 max:374283 total:56897588
min:321668 max:373622 total:55799061
min:336575 max:387027 total:58948777
min:350269 max:397098 total:61510405
min:336949 max:382367 total:58640224
min:327913 max:371026 total:56833639
min:322377 max:375011 total:56923970
min:354508 max:399130 total:61628878
min:319998 max:367493 total:55624467
min:337322 max:379689 total:58425775
min:325701 max:369950 total:56382432
min:318423 max:364997 total:55662597
min:332930 max:374174 total:57881582
min:324787 max:371432 total:56881287
min:335136 max:381850 total:58661101
min:329253 max:377998 total:58146731
min:353550 max:399807 total:61031126
min:312443 max:358633 total:55092296
min:344435 max:396344 total:61129639
min:332426 max:394539 total:58307766
min:322235 max:367385 total:56477056
min:326722 max:362761 total:55421905
min:318183 max:366510 total:56260638
min:321812 max:372084 total:56639167
min:328016 max:379484 total:57794343
min:314929 max:364644 total:55440152
average:57710064

3c8fb50445833b93f69b6b703a29aae3523cad0c
with paul's early version and the magic 7:
root@bigbox:~/will-it-scale# ./open1_processes -t 160 -s 30
testcase:Separate file open/close
warmup
min:310891 max:364268 total:54015547
min:283886 max:333177 total:49992270
min:275451 max:314699 total:47775422
min:275164 max:316351 total:47720614
min:283434 max:326614 total:49156206
min:276475 max:320313 total:48469874
measurement
min:274589 max:323239 total:48149462
min:280194 max:328827 total:49338289
min:277830 max:327060 total:48962337
min:281689 max:325917 total:49211850
min:271332 max:308350 total:46813631
min:275384 max:319016 total:47366390
min:276728 max:318277 total:47752679
min:275616 max:317111 total:47955871
min:278882 max:319082 total:47864449
min:267076 max:312427 total:47225886
min:279400 max:322798 total:48561113
min:279140 max:317367 total:47762975
min:278772 max:325575 total:49001990
min:271660 max:311780 total:47349871
min:283508 max:326299 total:49516078
min:284946 max:327525 total:49468752
min:271924 max:316507 total:47867902
min:279669 max:313937 total:47582153
min:272887 max:319545 total:47725521
min:281685 max:323791 total:48620478
min:280714 max:324849 total:48804594
min:283307 max:327424 total:49153787
min:280186 max:323924 total:48618088
min:270821 max:311985 total:47194656
min:282145 max:327910 total:48728398
min:276035 max:326523 total:48895232
min:275433 max:317441 total:48054952
min:276840 max:320486 total:48297727
min:280297 max:320323 total:48736783
min:286099 max:327522 total:50318962
average:48363361