[sheepdog] [sheepdog/sheepdog] 9afe75: sheep: create a dedicated workqueue for peer reque...

[Hitoshi Mitake]

Branch: refs/heads/peer-wq
Home: https://github.com/sheepdog/sheepdog
Commit: 9afe751e671d9e5913399a2c46a2c23a30d60008
https://github.com/sheepdog/sheepdog/commit/9afe751e671d9e5913399a2c46a2c23a30d60008
Author: Hitoshi Mitake <***@lab.ntt.co.jp>
Date: 2017-02-16 (Thu, 16 Feb 2017)

Changed paths:
M sheep/request.c
M sheep/sheep.c
M sheep/sheep_priv.h

Log Message:
-----------
sheep: create a dedicated workqueue for peer requests

Current sheepdog uses the io workqueue (sys->io_wqueue) for 2 kinds of
requests: peer and local. However, this architecture can cause
deadlock in the fixed workqueue mode because of the schedules like
below:

1. node A receives a request Ra from a client, queue Ra to io_wqueue
as a peer request
2. node B receives a request Rb from another client, queue Rb to
io_wqueue as a peer request
3. in node A, Ra forwards the requests to node B
4. in node B, Rb forwards the requests to node A
5. if node A or node B don't have idle workers in io_workqueue, it can
cause deadlock

This commit avoids the problem by creating a new dedicated workqueue
sys->peer_wqueue for avoiding the problem.

Signed-off-by: Hitoshi Mitake <***@lab.ntt.co.jp>