Drop in throughput by 27% for eventing - single function src bkt mutation test

We are seeing a drop in throughput for the test -

Functions executed/sec, 1 bucket x 100M x 1KB, 4KV + 1Eventing node, single function-BucketOp Source bkt mutation 

The test is setup as follows : 

1. Create the source bucket (bucket1) and metadata bucket (eventing)
2. Deploy eventing function which is listening on bucket1 for mutations and applying mutations on the same source bucket bucket1 after executing the function. 
3. Load 100M Docs on bucket1 and record throughput of the eventing function using the on_update_success stat of eventing.
4. After loading 100M Docs, apply access phase mutations on the same bucket1

The regression is seen in 7.0.0-4245

Stats Comparison : http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=themis_700-4241_load_access_and_wait_1743&snapshot=themis_700-4245_load_access_and_wait_9f03 

The CPU Utilization reduces during the access phase of the test where we apply mutations on the bucket1 as well as the ops rate