These lines are from durThread method in dur.cpp:

// commit sooner if one or more getLastError j:true is pending
sleepmillis(oneThird);
for( unsigned i = 1; i <= 2; i++ ) {
if( commitJob._notify.nWaiting() )
break;

As oneThird can't be less than 1 ms, every single write with j=true is penalized by that time. Should we move this check before sleepmillis?

if( !commitJob._notify.nWaiting() ) {
sleepmillis(oneThird);
for( unsigned i = 1; i <= 2; i++ ) {