Rephrase the docs for GCWork::do_work

src/scheduler/work.rs

@@ -14,11 +14,15 @@ use std::any::{type_name, TypeId};
 pub trait GCWork<VM: VMBinding>: 'static + Send {
  /// Define the work for this packet. However, this is not supposed to be called directly.
  /// Usually `do_work_with_stat()` should be used.
- /// Only call this method if you would like to explicitly execute a work packet in the current context
- /// (the given worker, and the current work packet). The statistics collected for executing the work are
- /// counted into the current context. This is NOT the normal way to execute a work packet: most work packets
- /// are polled and executed in the worker's main loop ([`GCWorker::run`]) using `do_work_with_stat`.
- /// This method should only be called directly if you would like to explicitly execute a work packet under the current context.
+ ///
+ /// Most work packets are polled and executed in the worker's main loop ([`GCWorker::run`])
+ /// using `do_work_with_stat`. If `do_work` is called directly during the execution of another
+ /// work packet, bypassing `do_work_with_stat()`, this work packet will not be counted into the
+ /// number of work packets executed, and the execution time of this work packet will be counted
+ /// as part of the execution time of the other work packet. Only call this method directly if
+ /// this is what you intend. But you should always consider adding the work packet
+ /// into a bucket so that other GC workers can execute it in parallel, unless the context-
+ /// switching overhead is a problem.
  fn do_work(&mut self, worker: &mut GCWorker<VM>, mmtk: &'static MMTK<VM>);
 
  /// Do work and collect statistics. This internally calls `do_work()`. In most cases,