[Qemu-devel] [RFC PATCH 0/9] Second threading model.

[Arun R Bharadwaj <arun@linux.vnet.ibm.com>]

Hi,

This patch implements the second threading model.
The first model can be referred here:
http://www.mail-archive.com/qemu-devel@nongnu.org/msg43846.html

The features of the second threading model:

* The VCPU thread runs the Qemu code until the first blocking
  call is encountered.

* The work to be done in the blocking call is assigned to an
  asynchronous thread and the VCPU thread continues running
  the Qemu code.

* If any blocking call is encountered by the asynchronous thread,
  it simply waits for the blocking call to finish and continues
  to run the succeeding part after that.

* There is no constant context switching between the VCPU thread
  and the asynchronous thread.

* The code flow is simple to understand when compared to the
  first threading model.

I have run the following test to measure the performance:

To test the v9fs_write call which is converted to the
second threading model, I run X dd threads in parallel
on the virtfs exported directory. The following is the command
I use for running 2 dd threads in parallel:

time dd if=/dev/zero of=null1 bs=4k count=1000 oflag=sync &
time dd if=/dev/zero of=null1 bs=4k count=1000 oflag=sync

Here is how the performance comparison between the original code,
first threading model and second threading model looks like:

                                  1       2      3      5      10

no threading:   real time(s)     18.1    46.4   99.2   360.8   1518.6
                system time(s)   18.0    38.3   66.8   211.7   551.6
                throughput(kbps) 226     353    373    235     268

1st model:      real time        18.8    48.6   77.7   164.5   451.3
                system time       0.6     0.2    0.18    0.68  2.4
                throughput       218     336    474     624    914

2nd model:      real time        23.1    37.8   57.1    166.5  430
                system time       0.9     1.8    0.24     0.7  3.0
                throughput       177     432    430      611   940


This patchset needs to be applied on top of the threadlets infrastructure
series available here:
http://www.mail-archive.com/qemu-devel@nongnu.org/msg43842.html

The following series implements...

---

Sripathi Kodi (9):
      Add read-write lock to QEMU
      Introduce lock fid_list_lock to protect the fid list.
      Global rename lock
      Convert stat into 2nd threading model
      Convert wstat into 2nd threading model
      Convert open into 2nd threading model
      Convert walk into 2nd threading model
      Convert read into 2nd threading model
      Convert write into 2nd threading model.


 hw/virtio-9p.c |  950 +++++++++++++++++++++++---------------------------------
 hw/virtio-9p.h |   27 ++
 qemu-thread.c  |   40 ++
 qemu-thread.h  |   10 +
 4 files changed, 463 insertions(+), 564 deletions(-)

-- 
arun