[PATCH v4 4/5] lxc: Implement virtual /proc/cpuinfo via LXC fuse

Julio Faracco jcfaracco at gmail.com
Thu Feb 27 15:00:08 UTC 2020


Thanks for your comments, Daniel.

Well, since you have a consensus about /proc/cpuinfo, I will only
resubmit the patches related to timer.

Julio Cesar Faracco

Em ter., 25 de fev. de 2020 às 08:34, Daniel P. Berrangé
<berrange at redhat.com> escreveu:
>
> On Mon, Feb 24, 2020 at 11:24:28AM -0300, Julio Faracco wrote:
> > This commit tries to fix lots of issues related to LXC VCPUs. One of
> > them is related to /proc/cpuinfo content. If only 1 VCPU is set, LXC
> > containers will show all CPUs available for host. The second one is
> > related to CPU share, if an user set only 1 VCPU, the container/process
> > will use all available CPUs. (This is not the case when `cpuset`
> > attribute is declared). So, this commit adds a virtual cpuinfo based on
> > VCPU mapping and it automatically limits the CPU usage according VCPU
> > count.
> >
> > Example (now):
> > LXC container - 8 CPUS with 2 VCPU:
> >     lxc-root# stress --cpu 8
> >
> > On host machine, only CPU 0 and 1 have 100% usage.
> >
> > Signed-off-by: Julio Faracco <jcfaracco at gmail.com>
> > ---
> >  src/lxc/lxc_cgroup.c    | 31 ++++++++++++++
> >  src/lxc/lxc_container.c | 39 ++++++++++-------
> >  src/lxc/lxc_fuse.c      | 95 ++++++++++++++++++++++++++++++++++++++---
> >  3 files changed, 145 insertions(+), 20 deletions(-)
> >
> > diff --git a/src/lxc/lxc_cgroup.c b/src/lxc/lxc_cgroup.c
> > index d29b65092a..912a252473 100644
> > --- a/src/lxc/lxc_cgroup.c
> > +++ b/src/lxc/lxc_cgroup.c
> > @@ -50,6 +50,34 @@ static int virLXCCgroupSetupCpuTune(virDomainDefPtr def,
> >  }
> >
> >
> > +static int virLXCCgroupSetupVcpuAuto(virDomainDefPtr def,
> > +                                     virCgroupPtr cgroup)
> > +{
> > +    size_t i;
> > +    int vcpumax;
> > +    virBuffer buffer = VIR_BUFFER_INITIALIZER;
> > +    virBufferPtr cpuset = &buffer;
> > +
> > +    vcpumax = virDomainDefGetVcpusMax(def);
> > +    for (i = 0; i < vcpumax; i++) {
> > +        virDomainVcpuDefPtr vcpu = virDomainDefGetVcpu(def, i);
> > +        /* Cgroup is smart enough to convert numbers separated
> > +         * by comma into ranges. Example: "0,1,2,5," -> "0-2,5".
> > +         * Libvirt does not need to process it here. */
> > +        if (vcpu)
> > +            virBufferAsprintf(cpuset, "%zu,", i);
> > +    }
>
> If I have 4 containers, each with vcpu==2, then all 4 containers
> are going to be taskset onto host CPUs 0 & 1, and host CPUs 2,3,4,5,6,7
> are going to be unused. This is not viable as a strategy.
>
> > +    if (virCgroupSetCpusetCpus(cgroup,
> > +                               virBufferCurrentContent(cpuset)) < 0) {
> > +        virBufferFreeAndReset(cpuset);
> > +        return -1;
> > +    }
> > +
> > +    virBufferFreeAndReset(cpuset);
> > +    return 0;
> > +}
>
> > +static int
> > +lxcProcReadCpuinfoParse(virDomainDefPtr def, char *base,
> > +                        virBufferPtr new_cpuinfo)
> > +{
> > +    char *procline = NULL;
> > +    char *saveptr = base;
> > +    size_t cpu;
> > +    size_t nvcpu;
> > +    size_t curcpu = 0;
> > +    bool get_proc = false;
> > +
> > +    nvcpu = virDomainDefGetVcpus(def);
> > +    while ((procline = strtok_r(NULL, "\n", &saveptr))) {
> > +        if (sscanf(procline, "processor\t: %zu", &cpu) == 1) {
>
> This doesn't work because it is assuming the /proc/cpuinfo data format
> for x86 architecture. Every architecture puts different info in this
> file, and only some of them using "processor: NN" as a delimiter for
> new entries. There's many examples in tests/sysinfodata/ and
> in tests/virhostcpudata/ showing this problem
>
> We had considered taking /proc/cpuinfo in the past, but decided against
> it. Since this file is non-standard data format varying across arches,
> well written apps won't actually look at /proc/cpuinfo at all. Instead
> they'll use /sys/devices/system/cpu instead.  I don't think we want to
> make /proc/cpuinfo be inconsistent with data in sysfs.
>
>
> > +            virDomainVcpuDefPtr vcpu = virDomainDefGetVcpu(def, cpu);
> > +            /* VCPU is mapped */
> > +            if (vcpu) {
> > +                if (curcpu == nvcpu)
> > +                    break;
> > +
> > +                if (curcpu > 0)
> > +                    virBufferAddLit(new_cpuinfo, "\n");
> > +
> > +                virBufferAsprintf(new_cpuinfo, "processor\t: %zu\n",
> > +                                  curcpu);
> > +                curcpu++;
> > +                get_proc = true;
> > +            } else {
> > +                get_proc = false;
> > +            }
> > +        } else {
> > +            /* It is not a processor index */
> > +            if (get_proc)
> > +                virBufferAsprintf(new_cpuinfo, "%s\n", procline);
> > +        }
> > +    }
> > +
> > +    virBufferAddLit(new_cpuinfo, "\n");
> > +
> > +    return strlen(virBufferCurrentContent(new_cpuinfo));
> > +}
>
> Regards,
> Daniel
> --
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