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Re: [Xen-devel] [PATCH RFC 31/49] xen/sched: use sched_resource cpu instead smp_processor_id in schedulers
- To: Juergen Gross <jgross@xxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 29 Mar 2019 19:36:40 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Robert VanVossen <robert.vanvossen@xxxxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Josh Whitehead <josh.whitehead@xxxxxxxxxxxxxxx>, Meng Xu <mengxu@xxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- Delivery-date: Fri, 29 Mar 2019 19:36:55 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 29/03/2019 15:09, Juergen Gross wrote:
> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
> index 9b5527c1eb..0b5e5e566b 100644
> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -347,7 +347,7 @@ int sched_init_vcpu(struct vcpu *v)
> if ( (item = sched_alloc_item(v)) == NULL )
> return 1;
>
> - if ( is_idle_domain(d) || d->is_pinned )
> + if ( is_idle_domain(d) )
> processor = v->vcpu_id;
> else
> processor = sched_select_initial_cpu(v);
This looks like a spurious change. I also don't an obvious other patch
that it might fit into.
As for the field itself, it is also fairly objectionable. It is only
ever set for the hardware domain, and only if dom0_vcpus_pin is used,
but the actual pinning information is also reflected in dom0's hard
affinity mask.
In practice, all this flag does is permit the use of VCPUOP_get_physid,
disallow the use of vcpu_set_hard_affinity(), and allow dom0 to attempt
to actually write to MSR_AMD64_NB_CFG, MSR_FAM10H_MMIO_CONF_BASE,
MSR_IA32_UCODE_REV, MSR_IA32_THERM_CONTROL and
MSR_IA32_ENERGY_PERF_BIAS, rather than having the write silently discarded.
Dom0's use of those MSRs is dubious at best, and disabled by default,
*and* when active, also cross-checks with the hard affinity mask. Does
anyone use dom0_vcpus_pin in production?
I think there is quite a lot of value in getting rid of d->is_pinned and
is_pinned_vcpu() entirely, with will remove an extreme
corner-case-x86-ism out of the common code.
~Andrew
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