[Qemu-block] [PATCH 0/3] mirror: Fix guest responsiveness during bitmap scan

[Fam Zheng]

This supersedes:

http://patchwork.ozlabs.org/patch/491415/

and [1] which is currently in Jeff's tree.

Although [1] fixed the QMP responsiveness, Alexandre DERUMIER reported that
guest responsiveness still suffers when we are busy in the initial dirty bitmap
scanning loop of mirror job. That is because 1) we issue too many lseeks; 2) we
only sleep for 0 ns which turns out quite ineffective in yielding BQL to vcpu
threads.  Both are fixed.

To reproduce: start a guest, attach a 10G raw image, then mirror it.  Your
guest will immediately start to stutter (with patch [1] testing on a local ext4
raw image, and "while echo -n .; do sleep 0.05; done" in guest console).

This series adds block_job_relax_cpu as suggested by Stefan Hajnoczi and uses
it in mirror job; and lets bdrv_is_allocated_above return a larger p_num as
suggested by Paolo Bonzini (although it's done without changing the API).

[1]: http://patchwork.ozlabs.org/patch/471656/ "block/mirror: Sleep
     periodically during bitmap scanning"

Fam Zheng (3):
  blockjob: Introduce block_job_relax_cpu
  mirror: Use block_job_relax_cpu during bitmap scanning
  mirror: Speed up bitmap initial scanning

 block/mirror.c           | 17 +++++++----------
 include/block/blockjob.h | 16 ++++++++++++++++
 2 files changed, 23 insertions(+), 10 deletions(-)

-- 
2.4.3