Why are builds on HGFS so slow?

My configuration

I work at a company whose product builds and runs exclusively on Linux. Like most sane people, I prefer to live in a more user-friendly operating system and my laptop runs Mac OSX. To build my company's product, I use VMWare Fusion to run an Ubuntu 14.04 virtual machine. I use a local GUI to edit and search source code, only using the virtual machine to compile and test the built product.

Until recently, I kept the files on my virtual machine in sync with the files on the host machine by using VMWares hgfs kernel module, which allows a guest to access files on the host (and vice versa). This configuration causes me no end of grief -- the open-vm-tools ubuntu package does not include hgfs so I have to manually compile and install VMWare's tools. This sometimes breaks and needs to be recompiled every time I update my kernel.

HGFS performance issues

On top of this, the VMWare HGFS has some serious performance issues. Yesterday, I got fed up with the fact that my incremental builds were slower than my colleagues and started doing a performance investigation. An incremental build in which no files were changed after a successful build took almost 10 seconds. I noticed my system had incredibly high CPU utilization and generated a Flame Graph:

I was amazed -- all the HGFS stacks were spending time blocked in mutex_spin_on_owner. It looks like all file accesses have to go through a filesystem-wide global lock!

HgfsTransportSendRequest(HgfsReq *req)   // IN: Request to send
    HgfsReq *origReq = req;
    int ret = -EIO;

    ASSERT(req->state == HGFS_REQ_STATE_UNSENT);                                    
    ASSERT(req->payloadSize <= req->bufferSize);


Once I realized this horrible performance pathology, I knew I couldn't use VMWare HGFS anymore. I set up Mac OSX to share the directory over nfs:

$ # Only share on the vmnet8 subnet and map all accesses to be my user.
$ echo "/Volumes/Developer -network -mask -mapall=areece" | sudo tee -a /etc/exports
$ sudo nfsd update

and mounted the directory on Linux:

$ echo " /mnt/Developer nfs" | sudo tee -a /etd/fstab
$ sudo mount

This cut my build times down to 1s, almost 10x faster. Here is the revised Flame Graph:

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