Re: [Xen-devel] [PATCH] libxl: avoid considering pCPUs outside of the cpupool during NUMA placement

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Oct 21, 2016 at 12:50:58PM +0200, Juergen Gross wrote:
> On 21/10/16 12:29, Wei Liu wrote:
> > On Fri, Oct 21, 2016 at 11:56:14AM +0200, Dario Faggioli wrote:
> >> During NUMA automatic placement, the information
> >> of how many vCPUs can run on what NUMA nodes is used,
> >> in order to spread the load as evenly as possible.
> >>
> >> Such information is derived from vCPU hard and soft
> >> affinity, but that is not enough. In fact, affinity
> >> can be set to be a superset of the pCPUs that belongs
> >> to the cpupool in which a domain is but, of course,
> >> the domain will never run on pCPUs outside of its
> >> cpupool.
> >>
> >> Take this into account in the placement algorithm.
> >>
> >> Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> >> Reported-by: George Dunlap <george.dunlap@xxxxxxxxxx>
> >> ---
> >> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> >> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> >> Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
> >> Cc: Juergen Gross <jgross@xxxxxxxx>
> >> Cc: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
> >> ---
> >> Wei, this is bugfix, so I think it should go in 4.8.
> >>
> > 
> > Yes. I agree.
> > 
> >> Ian, this is bugfix, so I think it is a backporting candidate.
> >>
> >> Also, note that this function does not respect the libxl coding style, as 
> >> far
> >> as error handling is concerned. However, given that I'm asking for it to 
> >> go in
> >> now and to be backported, I've tried to keep the changes to the minimum.
> >>
> >> I'm up for a follow up patch for 4.9 to make the style compliant.
> >>
> >> Thanks, Dario
> >> ---
> >>  tools/libxl/libxl_numa.c |   25 ++++++++++++++++++++++---
> >>  1 file changed, 22 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/tools/libxl/libxl_numa.c b/tools/libxl/libxl_numa.c
> >> index 33289d5..f2a719d 100644
> >> --- a/tools/libxl/libxl_numa.c
> >> +++ b/tools/libxl/libxl_numa.c
> >> @@ -186,9 +186,12 @@ static int nr_vcpus_on_nodes(libxl__gc *gc, 
> >> libxl_cputopology *tinfo,
> >>  {
> >>      libxl_dominfo *dinfo = NULL;
> >>      libxl_bitmap dom_nodemap, nodes_counted;
> >> +    libxl_cpupoolinfo cpupool_info;
> >>      int nr_doms, nr_cpus;
> >>      int i, j, k;
> >>  
> >> +    libxl_cpupoolinfo_init(&cpupool_info);
> >> +
> > 
> > Please move this into the loop below, see (*).
> 
> Why? libxl_cpupoolinfo_dispose() will clear cpupool_info.
> 

One _init should pair with one _dipose.

Even _dispose is idempotent at the moment, it might not be so in the
future.

> > 
> >>      dinfo = libxl_list_domain(CTX, &nr_doms);
> >>      if (dinfo == NULL)
> >>          return ERROR_FAIL;
> >> @@ -205,12 +208,18 @@ static int nr_vcpus_on_nodes(libxl__gc *gc, 
> >> libxl_cputopology *tinfo,
> >>      }
> >>  
> >>      for (i = 0; i < nr_doms; i++) {
> >> -        libxl_vcpuinfo *vinfo;
> >> -        int nr_dom_vcpus;
> >> +        libxl_vcpuinfo *vinfo = NULL;
> > 
> > This is not necessary because vinfo is written right away.
> 
> No, the first "goto next" is before vinfo is being written.
> 

Yes, this is necessary. Thanks for catching this.

Wei.

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