[libvirt] [PATCH v2] qemu: Rework setting process affinity

[Daniel P. Berrangé]

On Thu, Jan 31, 2019 at 10:34:17AM +0100, Michal Privoznik wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1503284
> 
> The way we currently start qemu from CPU affinity POV is as
> follows:
> 
>   1) the child process is set affinity to all online CPUs (unless
>   some vcpu pinning was given in the domain XML)
> 
>   2) Once qemu is running, cpuset cgroup is configured taking
>   memory pinning into account
> 
> Problem is that we let qemu allocate its memory just anywhere in
> 1) and then rely in 2) to be able to move the memory to
> configured NUMA nodes. This might not be always possible (e.g.
> qemu might lock some parts of its memory) and is very suboptimal
> (copying large memory between NUMA nodes takes significant amount
> of time).
> 
> The solution is to set affinity to one of (in priority order):
>   - The CPUs associated with NUMA memory affinity mask
>   - The CPUs associated with emulator pinning
>   - All online host CPUs
> 
> Later (once QEMU has allocated its memory) we then change this
> again to (again in priority order):
>   - The CPUs associated with emulator pinning
>   - The CPUs returned by numad
>   - The CPUs associated with vCPU pinning
>   - All online host CPUs
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
> 
> diff to v1 (both points suggested by Dan):
> - Expanded the commit message
> - fixed qemuProcessGetAllCpuAffinity so that it returns online CPU map
>   only
> 
>  src/qemu/qemu_process.c | 132 +++++++++++++++++++---------------------
>  1 file changed, 63 insertions(+), 69 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange at redhat.com>


Regards,
Daniel
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