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Re: [Qemu-devel] [PATCH 06/11] target-i386: add socket/core/thread prope
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCH 06/11] target-i386: add socket/core/thread properties to X86CPU |
Date: |
Thu, 23 Jun 2016 18:43:53 -0300 |
User-agent: |
Mutt/1.6.1 (2016-04-27) |
On Thu, Jun 23, 2016 at 10:46:36PM +0200, Igor Mammedov wrote:
> On Thu, 23 Jun 2016 17:18:46 -0300
> Eduardo Habkost <address@hidden> wrote:
[...]
> > >
> > > >
> > > > I suggest validating the properties, and setting them in case
> > > > they are not set:
> > > >
> > > > x86_topo_ids_from_apicid(cpu->apic_id, smp_cores, smp_threads,
> > > > &topo);
> > > >
> > > > if (cpu->socket != -1 && cpu->socket != topo.socket_id) {
> > > > error_setg(errp, "CPU socket ID mismatch: ...");
> > > > return;
> > > > }
> > > > cpu->socket = topo.socket_id;
> > > >
> > > > if (cpu->core != -1 && cpu->core != topo.core_id) {
> > > > error_setg(errp, "CPU core ID mismatch: ...");
> > > > return;
> > > > }
> > > > cpu->core = topo.core_id;
> > > >
> > > > if (cpu->thread != -1 && cpu->thread != topo.smt_id) {
> > > > error_setg(errp, "CPU thread ID mismatch: ...");
> > > > return;
> > > > }
> > > > cpu->thread = topo.smt_id;
> > > >
> > > > We could do that inside x86_cpu_realizefn(), so that
> > > > socket/core/thread would be always set in all CPUs.
> > > all CPUs pass through pc_cpu_pre_plug() before cpu.relizefn()
> > > so I'd rather do it here at board level responsible for
> > > setting apic_id or socket/core/thread info is not set.
> >
> > Then *-user will be inconsistent, and will always have invalid
> > values in socket/core/thread. If one day we add any logic using
> > the socket/core/thread properties in cpu.c, it will break on
> > *-user.
> >
> > All those properties are X86CPU properties, meaning they are
> > input to the X86CPU code. I don't see why we should move logic
> > related to them outside cpu.c unless really necessary.
> >
> > (The apic-id calculation at patch 07/11, for example, is more
> > difficult to move to cpu.c, because the PC code needs the APIC ID
> > before calling realize. We could move it to the apic-id getter,
> > but I dislike having magic getter/setters and like that you made
> > it a static property.)
> set of socket/core/thread is a synonym for apic_id and it's board that
> manages and knows valid values for them.
The CPU already knows exactly what the bits inside APIC ID mean,
because it has to report topology information through CPUID.
> Putting above snippet into
> cpu.relizefn() would make CPU access globals smp_cores, smp_threads
> which are essentially machine_state and Drew working on moving them
> there and eliminating globals. So suddenly CPU would need to poke into
> machine object, and we return to the same state wrt *-user only with
> hack in cpu.c.
After Drew's code is included, we can simply use
CPUState::nr_cores and CPUState::nr_threads.
>
> I'd worry about -smp and *-user when it comes into that target as it
> will probably need apic_id and maybe socket/core/thread as well.
The point is to not even have to worry about *-user later, by
keeping both softmmu and *-user consistent. People reviewing
patches a few years from now probably wouldn't even notice that
code using the socket/core/thread fields will break in *-user.
I wouldn't mind about having the code in pc.c at all, if it
didn't make *-user inconsistent, or if the CPU object didn't had
all the required information yet. But I don't think it is
reasonable to intentionally leave X86CPU fields inconsistent in
*-user if we can easily fix it by moving initialization to
realizefn.
But if you are really strongly against that, I can propose that
as a follow-up later (after Drew's series is included).
--
Eduardo
- Re: [Qemu-devel] [PATCH 07/11] pc: set APIC ID based on socket/core/thread ids if it's not been set yet, (continued)
[Qemu-devel] [PATCH 05/11] target-i386: cpu: replace custom apic-id setter/getter with static property, Igor Mammedov, 2016/06/23
[Qemu-devel] [PATCH 06/11] target-i386: add socket/core/thread properties to X86CPU, Igor Mammedov, 2016/06/23
[Qemu-devel] [PATCH 08/11] pc: implement query-hotpluggable-cpus callback, Igor Mammedov, 2016/06/23
[Qemu-devel] [PATCH 09/11] pc: register created initial and hotpluged CPUs in one place pc_cpu_plug(), Igor Mammedov, 2016/06/23
[Qemu-devel] [PATCH 10/11] pc: delay setting number of boot CPUs to machine_done time, Igor Mammedov, 2016/06/23
[Qemu-devel] [PATCH 11/11] pc: cpu: allow device_add to be used with x86 cpu, Igor Mammedov, 2016/06/23