I'm seeing lots of these in the sharded cluster logs:
2015-08-31T07:52:28.150-0700 I WRITE [conn21429] update config.mongos query:

{ _id: "profile-001a.staging.dccl:27017" }

update: { $set:

{ ping: new Date(1441032748030), up: 2830090, waiting: false, mongoVersion: "3.0.5" }

} nscanned:1 nscannedObjects:1 nMatched:1 nModified:1 fastmod:1 keyUpdates:0 writeConflicts:0 numYields:0 locks:{ Global: { acquireCount:

{ r: 2, w: 2 }

}, MMAPV1Journal: { acquireCount:

{ w: 2 }

, acquireWaitCount:

{ w: 1 }

, timeAcquiringMicros:

{ w: 117320 }

}, Database: { acquireCount:

{ w: 2 }

}, Collection: { acquireCount:

{ W: 2 }

} } 117ms

2015-08-31T06:14:50.942-0700 I WRITE [conn21436] update config.mongos query:

{ _id: "profile-001b.staging.dccl:27017" }

update: { $set:

{ ping: new Date(1441026890836), up: 2823899, waiting: false, mongoVersion: "3.0.5" }

} nscanned:1 nscannedObjects:1 nMatched:1 nModified:1 fastmod:1 keyUpdates:0 writeConflicts:0 numYields:0 locks:{ Global: { acquireCount:

{ r: 2, w: 2 }

}, MMAPV1Journal: { acquireCount:

{ w: 2 }

, acquireWaitCount:

{ w: 1 }

, timeAcquiringMicros:

{ w: 104858 }

}, Database: { acquireCount:

{ w: 2 }

}, Collection: { acquireCount:

{ W: 2 }

} } 105ms

2015-08-30T22:46:05.694-0700 I WRITE [conn41724] update config.mongos query:

{ _id: "transaction-002b.prod.dccl:27017" }

update: { $set:

{ ping: new Date(1440999965536), up: 372470, waiting: false, mongoVersion: "3.0.6" }

} nscanned:1 nscannedObjects:1 nMatched:1 nModified:1 fastmod:1 keyUpdates:0 writeConflicts:0 numYields:0 locks:{ Global: { acquireCount:

{ r: 2, w: 2 }

}, MMAPV1Journal: { acquireCount:

{ w: 2 }

, acquireWaitCount:

{ w: 1 }

, timeAcquiringMicros:

{ w: 154476 }

}, Database: { acquireCount:

{ w: 2 }

}, Collection: { acquireCount:

{ W: 2 }

} } 154ms

2015-08-30T22:37:33.179-0700 I WRITE [conn7] update config.mongos query:

{ _id: "etl-001b.prod.dccl:27017" }

update: { $set:

{ ping: new Date(1440999453060), up: 7013430, waiting: false, mongoVersion: "3.0.2" }

} nscanned:1 nscannedObjects:1 nMatched:1 nModified:1 fastmod:1 keyUpdates:0 writeConflicts:0 numYields:0 locks:{ Global: { acquireCount:

{ r: 2, w: 2 }

}, MMAPV1Journal: { acquireCount:

{ w: 2 }

, acquireWaitCount:

{ w: 1 }

, timeAcquiringMicros:

{ w: 116568 }

}, Database: { acquireCount:

{ w: 2 }

}, Collection: { acquireCount:

{ W: 2 }

} } 116ms
Why would these commands takes over 100ms to run and what are they ?