"Michael S. Tsirkin" [off-list ref] writes:

On Sat, Aug 08, 2015 at 07:06:38PM -0400, Bandan Das wrote:

quoted

Hi Michael,

...

quoted

quoted

- does the design address the issue of VM 1 being blocked
  (e.g. because it hits swap) and blocking VM 2?

Good question. I haven't thought of this yet. But IIUC,
the worker thread will complete VM1's job and then move on to
executing VM2's scheduled work.
It doesn't matter if VM1 is
blocked currently. I think it would be a problem though if/when
polling is introduced.

Sorry, I wasn't clear. If VM1's memory is in swap, attempts to
access it might block the service thread, so it won't
complete VM2's job.

Ah ok, I understand now. I am pretty sure the current RFC doesn't
take care of this :) I will add this to my todo list for v2.

Bandan

quoted

quoted

quoted

#* Last run with the vCPU and I/O thread(s) pinned, no CPU/memory limit imposed.
#  I/O thread runs on CPU 14 or 15 depending on which guest it's serving

There's a simple graph at
http://people.redhat.com/~bdas/elvis/data/results.png
that shows how task affinity results in a jump and even without it,
as the number of guests increase, the shared vhost design performs
slightly better.

Observations:
1. In terms of "stock" performance, the results are comparable.
2. However, with a tuned setup, even without polling, we see an improvement
with the new design.
3. Making the new design simulate old behavior would be a matter of setting
the number of guests per vhost threads to 1.
4. Maybe, setting a per guest limit on the work being done by a specific vhost
thread is needed for it to be fair.
5. cgroup associations needs to be figured out. I just slightly hacked the
current cgroup association mechanism to work with the new model. Ccing cgroups
for input/comments.

Many thanks to Razya Ladelsky and Eyal Moscovici, IBM for the initial
patches, the helpful testing suggestions and discussions.

Bandan Das (4):
  vhost: Introduce a universal thread to serve all users
  vhost: Limit the number of devices served by a single worker thread
  cgroup: Introduce a function to compare cgroups
  vhost: Add cgroup-aware creation of worker threads

 drivers/vhost/net.c    |   6 +-
 drivers/vhost/scsi.c   |  18 ++--
 drivers/vhost/vhost.c  | 272 +++++++++++++++++++++++++++++++++++--------------
 drivers/vhost/vhost.h  |  32 +++++-
 include/linux/cgroup.h |   1 +
 kernel/cgroup.c        |  40 ++++++++
 6 files changed, 275 insertions(+), 94 deletions(-)

-- 
2.4.3