It looks like a lot of mappings need adding as most people come up as unknown:

EDIT updated with newer mappings.

Top changeset contributors by employer
(Unknown)                 11190 (62.7%)
(None)                    4280 (24.0%)
Huawei                     862 (4.8%)
Ferrous Systems            630 (3.5%)
Academics (various)        563 (3.2%)
Red Hat                    124 (0.7%)
Google                     102 (0.6%)
Microsoft                   59 (0.3%)
IBM                         28 (0.2%)
Funky                       11 (0.1%)

Top lines changed by employer
(Unknown)                 1018418 (56.9%)
(None)                    484385 (27.0%)
Academics (various)       118247 (6.6%)
Ferrous Systems           100533 (5.6%)
Huawei                    45443 (2.5%)
Red Hat                   16009 (0.9%)
Microsoft                 3359 (0.2%)
Google                    2844 (0.2%)
Funky                      447 (0.0%)
IBM                        388 (0.0%)

the top contributors over the last year were:

Developers with the most changesets                                                                                                                                          
Michael Goulet            1027 (5.7%)                                                                                                                                        
Nicholas Nethercote        789 (4.4%)                                                                                                                                        
Ralf Jung                  763 (4.3%)                                                                                                                                        
Camille Gillot             727 (4.1%)                                                                                                                                        
Lukas Wirth                640 (3.6%)                                                                                                                                        
Guillaume Gomez            583 (3.3%)                                                                                                                                        
bjorn3                     550 (3.1%)                                                                                                                                        
Oliver Scherer             470 (2.6%)                                                                                                                                        
Michael Howell             293 (1.6%)                                                                                                                                        
Waffle Lapkin              266 (1.5%)                                                                                                                                        
Esteban Küber              251 (1.4%)                                                                                                                                        
Zalathar                   249 (1.4%)                                                                                                                                        
lcnr                       247 (1.4%)                                                                                                                                        
y21                        221 (1.2%)                                                                                                                                        
Jynn Nelson                188 (1.1%)                                                                                                                                        
Urgau                      187 (1.0%)                                                                                                                                        
Nilstrieb                  170 (1.0%)                                                                                                                                        
Centri3                    169 (0.9%)  
hamidreza kalbasi          164 (0.9%)
Pietro Albini              156 (0.9%)     

Developers with the most changed lines                                                
Laurențiu Nicola          163716 (9.1%)
Philipp Krones            118974 (6.6%)                                               
Lukas Wirth               100948 (5.6%)
Camille Gillot            94829 (5.3%)                                                
Oleksandr Babak           89625 (5.0%)
Michael Goulet            83965 (4.7%)                                                
Oliver Scherer            39890 (2.2%)
Nicholas Nethercote       39484 (2.2%)
Ralf Jung                 38113 (2.1%) 
hamidreza kalbasi         34576 (1.9%)
Ben Kimock                33647 (1.9%)
Guillaume Gomez           30774 (1.7%)
bjorn3                    29218 (1.6%)
Zalathar                  26214 (1.5%)
Esteban Küber             24612 (1.4%)
Alex Macleod              23724 (1.3%)
y21                       20447 (1.1%)
Centri3                   20168 (1.1%)
Urgau                     19964 (1.1%)
Michael Howell            19795 (1.1%)