Messages in this thread | | | From | "Zengtao (B)" <> | Subject | RE: [PATCH] cpu-topology: warn if NUMA configurations conflicts with lower layer | Date | Thu, 2 Jan 2020 12:47:01 +0000 |
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> -----Original Message----- > From: Sudeep Holla [mailto:sudeep.holla@arm.com] > Sent: Thursday, January 02, 2020 7:30 PM > To: Zengtao (B) > Cc: Linuxarm; Greg Kroah-Hartman; Rafael J. Wysocki; > linux-kernel@vger.kernel.org; Morten Rasmussen > Subject: Re: [PATCH] cpu-topology: warn if NUMA configurations conflicts > with lower layer > > On Thu, Jan 02, 2020 at 03:05:40AM +0000, Zengtao (B) wrote: > > Hi Sudeep: > > > > Thanks for your reply. > > > > > -----Original Message----- > > > From: Sudeep Holla [mailto:sudeep.holla@arm.com] > > > Sent: Wednesday, January 01, 2020 12:41 AM > > > To: Zengtao (B) > > > Cc: Linuxarm; Greg Kroah-Hartman; Rafael J. Wysocki; > > > linux-kernel@vger.kernel.org; Sudeep Holla; Morten Rasmussen > > > Subject: Re: [PATCH] cpu-topology: warn if NUMA configurations > conflicts > > > with lower layer > > > > > > On Mon, Dec 23, 2019 at 04:16:19PM +0800, z00214469 wrote: > > > > As we know, from sched domain's perspective, the DIE layer should > be > > > > larger than or at least equal to the MC layer, and in some cases, MC > > > > is defined by the arch specified hardware, MPIDR for example, but > > > NUMA > > > > can be defined by users, > > > > > > Who are the users you are referring above ? > > For example, when I use QEMU to start a guest linux, I can define the > > NUMA topology of the guest linux whatever i want. > > OK and how is the information passed to the kernel ? DT or ACPI ? > We need to fix the miss match if any during the initial parse of those > information. >
Both, For the current QEMU, we don't have the correct cpu topology passed to linux. Luckily drjones planed to deal with the issue. https://patchwork.ozlabs.org/cover/939301/
> > > > with the following system configrations: > > > > > > Do you mean ACPI tables or DT or some firmware tables ? > > > > > > > ************************************* > > > > NUMA: 0-2, 3-7 > > > > > > Is the above simply wrong with respect to hardware and it actually > match > > > core_siblings ? > > > > > Actually, we can't simply say this is wrong, i just want to show an > example. > > And this example also can be: > > NUMA: 0-23, 24-47 > > core_siblings: 0-15, 16-31, 32-47 > > > > Are you sure of the above ? Possible values w.r.t hardware config: > core_siblings: 0-15, 16-23, 24-31, 32-47 > > But what you have specified above is still wrong core_siblings IMO. > It depends on the hardware, on my platform, 16 cores per cluster.
> > [...] > > > > > diff --git a/drivers/base/arch_topology.c > b/drivers/base/arch_topology.c > > > > index 1eb81f11..5fe44b3 100644 > > > > --- a/drivers/base/arch_topology.c > > > > +++ b/drivers/base/arch_topology.c > > > > @@ -439,10 +439,18 @@ const struct cpumask > > > *cpu_coregroup_mask(int cpu) > > > > if (cpumask_subset(&cpu_topology[cpu].core_sibling, > core_mask)) { > > > > /* not numa in package, lets use the package siblings */ > > > > core_mask = &cpu_topology[cpu].core_sibling; > > > > - } > > > > + } else > > > > + pr_warn_once("Warning: suspicous broken topology: > cpu:[%d]'s > > > core_sibling:[%*pbl] not a subset of numa node:[%*pbl]\n", > > > > + cpu, > cpumask_pr_args(&cpu_topology[cpu].core_sibling), > > > > + cpumask_pr_args(core_mask)); > > > > + > > > > > > Won't this print warning on all systems that don't have numa within a > > > package ? What are you trying to achieve here ? > > > > Since in my case, when this corner case happens, the linux kernel just fall > into > > dead loop with no prompt, here this is a helping message will help a lot. > > > > As I said, wrong configurations need to be detected when generating > DT/ACPI if possible. The above will print warning on systems with NUMA > within package. > > NUMA: 0-7, 8-15 > core_siblings: 0-15 > > The above is the example where the die has 16 CPUs and 2 NUMA nodes > within a package, your change throws error to the above config which is > wrong. > From your example, the core 7 and core 8 has got different LLC but the same Low Level cache? From schedule view of point, lower level sched domain should be a subset of higher Level sched domain.
> > > > > > > if (cpu_topology[cpu].llc_id != -1) { > > > > if (cpumask_subset(&cpu_topology[cpu].llc_sibling, > core_mask)) > > > > core_mask = &cpu_topology[cpu].llc_sibling; > > > > + else > > > > + pr_warn_once("Warning: suspicous broken topology: > > > cpu:[%d]'s llc_sibling:[%*pbl] not a subset of numa node:[%*pbl]\n", > > > > + cpu, > > > cpumask_pr_args(&cpu_topology[cpu].llc_sibling), > > > > + cpumask_pr_args(core_mask)); > > > > } > > > > > > > > > > This will trigger warning on all systems that lack cacheinfo topology. > > > I don't understand the intent of this patch at all. Can you explain > > > all the steps you follow and the issue you face ? > > > > Can you show me an example, what I really want to warn is the case that > > NUMA topology conflicts with lower level. > > > > I was wrong here, I mis-read this section. I still fail to understand > why the above change is needed. I understood the QEMU example, but you > haven't specified how cacheinfo looks like there. >
My idea: (1) If the dtb/acpi is not legal, the linux kernel should check or prompt to help debug. (2)From scheduler view of point, low level sched domain should be a subset of high level Sched domain.
I am very sure about (2), any example to show me (2) is wrong?
Thanks. Zengtao
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