Mmm... this patch has a few hard-tabs in it! Apologies for that. :-/ I'm attaching a version without them, but I surely can resubmit the series with this fixed, it that's easier.
Regards, and Sorry again
On Tue, 2022-08-02 at 15:51 +0200, Dario Faggioli wrote:
> Right now, affinity for dom0 vCPUs is setup in two steps. This is a
> problem as, at least in Credit2, unit_insert() sees and uses the
> "intermediate" affinity, and place the vCPUs on CPUs where they
> cannot
> be run. And this in turn results in boot hangs, if the "dom0_nodes"
> parameter is used.
>
> Fix this by setting up the affinity properly once and for all, in
> sched_init_vcpu() called by create_vcpu().
>
> Note that, unless a soft-affinity is explicitly specified for dom0
> (by
> using the relaxed mode of "dom0_nodes") we set it to the default,
> which
> is all CPUs, instead of computing it basing on hard affinity (if
> any).
> This is because hard and soft affinity should be considered as
> independent user controlled properties. In fact, if we dor derive
> dom0's
> soft-affinity from its boot-time hard-affinity, such computed value
> will
> continue to be used even if later the user changes the hard-affinity.
> And this could result in the vCPUs behaving differently than what the
> user wanted and expects.
>
> Fixes: dafd936ddd ("Make credit2 the default scheduler")
> Reported-by: Olaf Hering <[email protected]>
> Signed-off-by: Dario Faggioli <[email protected]>
> ---
> Cc: Jan Beulich <[email protected]>
> Cc: George Dunlap <[email protected]>
> ---
> Changes from "RFC" [1]:
> - Moved handling of the shim case
> - Added some more explanation (in particular, about why we stick to
> all
> CPUs for the soft affinity) in both commit message and comment
> - Remove spurious (and non-necessary) credit2 change
>
> [1]
> https://lore.kernel.org/xen-devel/[email protected]/
> ---
> xen/common/sched/core.c | 63 +++++++++++++++++++++++++++++--------
> ----------
> 1 file changed, 39 insertions(+), 24 deletions(-)
>
> diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
> index 379a791d62..0585c643a5 100644
> --- a/xen/common/sched/core.c
> +++ b/xen/common/sched/core.c
> @@ -571,12 +571,46 @@ int sched_init_vcpu(struct vcpu *v)
> return 1;
> }
>
> - /*
> - * Initialize affinity settings. The idler, and potentially
> - * domain-0 VCPUs, are pinned onto their respective physical
> CPUs.
> - */
> - if ( is_idle_domain(d) || (is_control_domain(d) &&
> opt_dom0_vcpus_pin) )
> + if ( is_idle_domain(d) )
> + {
> + /* Idle vCPUs are always pinned onto their respective pCPUs
> */
> + sched_set_affinity(unit, cpumask_of(processor),
> &cpumask_all);
> + }
> + else if ( pv_shim && v->vcpu_id == 0 )
> + {
> + /*
> + * PV-shim: vcpus are pinned 1:1. Initially only 1 cpu is
> online,
> + * others will be dealt with when onlining them. This avoids
> pinning
> + * a vcpu to a not yet online cpu here.
> + */
> + sched_set_affinity(unit, cpumask_of(0), cpumask_of(0));
> + }
> + else if ( is_control_domain(d) && opt_dom0_vcpus_pin )
> + {
> + /*
> + * If dom0_vcpus_pin is specified, dom0 vCPUs are pinned 1:1
> to
> + * their respective pCPUs too.
> + */
> sched_set_affinity(unit, cpumask_of(processor),
> &cpumask_all);
> + }
> +#ifdef CONFIG_X86
> + else if ( is_control_domain(d) )
> + {
> + /*
> + * In absence of dom0_vcpus_pin instead, the hard and soft
> affinity of
> + * dom0 is controlled by the (x86 only) dom0_nodes
> parameter. At this
> + * point it has been parsed and decoded into the dom0_cpus
> mask.
> + *
> + * Note that we always honor what user explicitly requested,
> for both
> + * hard and soft affinity, without doing any dynamic
> computation of
> + * either of them.
> + */
> + if ( !dom0_affinity_relaxed )
> + sched_set_affinity(unit, &dom0_cpus, &cpumask_all);
> + else
> + sched_set_affinity(unit, &cpumask_all, &dom0_cpus);
> + }
> +#endif
> else
> sched_set_affinity(unit, &cpumask_all, &cpumask_all);
>
> @@ -3402,29 +3436,10 @@ void wait(void)
> void __init sched_setup_dom0_vcpus(struct domain *d)
> {
> unsigned int i;
> - struct sched_unit *unit;
>
> for ( i = 1; i < d->max_vcpus; i++ )
> vcpu_create(d, i);
>
> - /*
> - * PV-shim: vcpus are pinned 1:1.
> - * Initially only 1 cpu is online, others will be dealt with
> when
> - * onlining them. This avoids pinning a vcpu to a not yet online
> cpu here.
> - */
> - if ( pv_shim )
> - sched_set_affinity(d->vcpu[0]->sched_unit,
> - cpumask_of(0), cpumask_of(0));
> - else
> - {
> - for_each_sched_unit ( d, unit )
> - {
> - if ( !opt_dom0_vcpus_pin && !dom0_affinity_relaxed )
> - sched_set_affinity(unit, &dom0_cpus, NULL);
> - sched_set_affinity(unit, NULL, &dom0_cpus);
> - }
> - }
> -
> domain_update_node_affinity(d);
> }
> #endif
>
>
>
--
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
-------------------------------------------------------------------
<<This happens because _I_ choose it to happen!>> (Raistlin Majere)
From 52fd2b18f6a396f56e1f70f842360c9a8daa7ef7 Mon Sep 17 00:00:00 2001 From: Dario Faggioli <[email protected]> Date: Wed, 27 Apr 2022 13:21:30 +0200 Subject: [PATCH 2/2] xen/sched: setup dom0 vCPUs affinity only once Right now, affinity for dom0 vCPUs is setup in two steps. This is a problem as, at least in Credit2, unit_insert() sees and uses the "intermediate" affinity, and place the vCPUs on CPUs where they cannot be run. And this in turn results in boot hangs, if the "dom0_nodes" parameter is used. Fix this by setting up the affinity properly once and for all, in sched_init_vcpu() called by create_vcpu(). Note that, unless a soft-affinity is explicitly specified for dom0 (by using the relaxed mode of "dom0_nodes") we set it to the default, which is all CPUs, instead of computing it basing on hard affinity (if any). This is because hard and soft affinity should be considered as independent user controlled properties. In fact, if we dor derive dom0's soft-affinity from its boot-time hard-affinity, such computed value will continue to be used even if later the user changes the hard-affinity. And this could result in the vCPUs behaving differently than what the user wanted and expects. Fixes: dafd936ddd ("Make credit2 the default scheduler") Reported-by: Olaf Hering <[email protected]> Signed-off-by: Dario Faggioli <[email protected]> --- Cc: Jan Beulich <[email protected]> Cc: George Dunlap <[email protected]> --- Changes from "RFC" [1]: - Moved handling of the shim case - Added some more explanation (in particular, about why we stick to all CPUs for the soft affinity) in both commit message and comment - Remove spurious (and non-necessary) credit2 change [1] https://lore.kernel.org/xen-devel/[email protected]/ --- xen/common/sched/core.c | 63 +++++++++++++++++++++++++---------------- 1 file changed, 39 insertions(+), 24 deletions(-) diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c index 379a791d62..b79c3dda66 100644 --- a/xen/common/sched/core.c +++ b/xen/common/sched/core.c @@ -571,12 +571,46 @@ int sched_init_vcpu(struct vcpu *v) return 1; } - /* - * Initialize affinity settings. The idler, and potentially - * domain-0 VCPUs, are pinned onto their respective physical CPUs. - */ - if ( is_idle_domain(d) || (is_control_domain(d) && opt_dom0_vcpus_pin) ) + if ( is_idle_domain(d) ) + { + /* Idle vCPUs are always pinned onto their respective pCPUs */ + sched_set_affinity(unit, cpumask_of(processor), &cpumask_all); + } + else if ( pv_shim && v->vcpu_id == 0 ) + { + /* + * PV-shim: vcpus are pinned 1:1. Initially only 1 cpu is online, + * others will be dealt with when onlining them. This avoids pinning + * a vcpu to a not yet online cpu here. + */ + sched_set_affinity(unit, cpumask_of(0), cpumask_of(0)); + } + else if ( is_control_domain(d) && opt_dom0_vcpus_pin ) + { + /* + * If dom0_vcpus_pin is specified, dom0 vCPUs are pinned 1:1 to + * their respective pCPUs too. + */ sched_set_affinity(unit, cpumask_of(processor), &cpumask_all); + } +#ifdef CONFIG_X86 + else if ( is_control_domain(d) ) + { + /* + * In absence of dom0_vcpus_pin instead, the hard and soft affinity of + * dom0 is controlled by the (x86 only) dom0_nodes parameter. At this + * point it has been parsed and decoded into the dom0_cpus mask. + * + * Note that we always honor what user explicitly requested, for both + * hard and soft affinity, without doing any dynamic computation of + * either of them. + */ + if ( !dom0_affinity_relaxed ) + sched_set_affinity(unit, &dom0_cpus, &cpumask_all); + else + sched_set_affinity(unit, &cpumask_all, &dom0_cpus); + } +#endif else sched_set_affinity(unit, &cpumask_all, &cpumask_all); @@ -3402,29 +3436,10 @@ void wait(void) void __init sched_setup_dom0_vcpus(struct domain *d) { unsigned int i; - struct sched_unit *unit; for ( i = 1; i < d->max_vcpus; i++ ) vcpu_create(d, i); - /* - * PV-shim: vcpus are pinned 1:1. - * Initially only 1 cpu is online, others will be dealt with when - * onlining them. This avoids pinning a vcpu to a not yet online cpu here. - */ - if ( pv_shim ) - sched_set_affinity(d->vcpu[0]->sched_unit, - cpumask_of(0), cpumask_of(0)); - else - { - for_each_sched_unit ( d, unit ) - { - if ( !opt_dom0_vcpus_pin && !dom0_affinity_relaxed ) - sched_set_affinity(unit, &dom0_cpus, NULL); - sched_set_affinity(unit, NULL, &dom0_cpus); - } - } - domain_update_node_affinity(d); } #endif -- 2.37.1
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