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

[Stefan Hajnoczi]

On Thu, Jul 09, 2015 at 11:47:55AM +0800, Fam Zheng wrote:
> 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(-)

This patch only converts the mirror block job to use the new relax
function.  The other block jobs (stream, backup, commit) are still using
a 0 ns delay and are therefore broken.  They should probably be
converted in the same series.

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