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Re: [PATCH v6 4/6] xen/cpupool: Create different cpupools at boot time



On Fri, 8 Apr 2022, Luca Fancellu wrote:
> Introduce a way to create different cpupools at boot time, this is
> particularly useful on ARM big.LITTLE system where there might be the
> need to have different cpupools for each type of core, but also
> systems using NUMA can have different cpu pools for each node.
> 
> The feature on arm relies on a specification of the cpupools from the
> device tree to build pools and assign cpus to them.
> 
> ACPI is not supported for this feature.
> 
> Documentation is created to explain the feature.
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> Changes in v6:
> - Changed docs, return if booted with ACPI in btcpupools_dtb_parse,
>   panic if /chosen does not exists. Changed commit message (Julien)
> - Add Juergen R-by for the xen/common/sched part that didn't change
> Changes in v5:
> - Fixed wrong variable name, swapped schedulers, add scheduler info
>   in the printk (Stefano)
> - introduce assert in cpupool_init and btcpupools_get_cpupool_id to
>   harden the code
> Changes in v4:
> - modify Makefile to put in *.init.o, fixed stubs and macro (Jan)
> - fixed docs, fix brakets (Stefano)
> - keep cpu0 in Pool-0 (Julien)
> - moved printk from btcpupools_allocate_pools to
>   btcpupools_get_cpupool_id
> - Add to docs constraint about cpu0 and Pool-0
> Changes in v3:
> - Add newline to cpupools.txt and removed "default n" from Kconfig (Jan)
> - Fixed comment, moved defines, used global cpu_online_map, use
>   HAS_DEVICE_TREE instead of ARM and place arch specific code in header
>   (Juergen)
> - Fix brakets, x86 code only panic, get rid of scheduler dt node, don't
>   save pool pointer and look for it from the pool list (Stefano)
> - Changed data structures to allow modification to the code.
> Changes in v2:
> - Move feature to common code (Juergen)
> - Try to decouple dtb parse and cpupool creation to allow
>   more way to specify cpupools (for example command line)
> - Created standalone dt node for the scheduler so it can
>   be used in future work to set scheduler specific
>   parameters
> - Use only auto generated ids for cpupools
> ---
>  docs/misc/arm/device-tree/cpupools.txt | 140 +++++++++++++++++
>  xen/arch/arm/include/asm/smp.h         |   3 +
>  xen/common/Kconfig                     |   7 +
>  xen/common/Makefile                    |   1 +
>  xen/common/boot_cpupools.c             | 207 +++++++++++++++++++++++++
>  xen/common/sched/cpupool.c             |  12 +-
>  xen/include/xen/sched.h                |  14 ++
>  7 files changed, 383 insertions(+), 1 deletion(-)
>  create mode 100644 docs/misc/arm/device-tree/cpupools.txt
>  create mode 100644 xen/common/boot_cpupools.c
> 
> diff --git a/docs/misc/arm/device-tree/cpupools.txt 
> b/docs/misc/arm/device-tree/cpupools.txt
> new file mode 100644
> index 000000000000..40cc8135c66f
> --- /dev/null
> +++ b/docs/misc/arm/device-tree/cpupools.txt
> @@ -0,0 +1,140 @@
> +Boot time cpupools
> +==================
> +
> +When BOOT_TIME_CPUPOOLS is enabled in the Xen configuration, it is possible 
> to
> +create cpupools during boot phase by specifying them in the device tree.
> +ACPI is not supported for this feature.
> +
> +Cpupools specification nodes shall be direct childs of /chosen node.
> +Each cpupool node contains the following properties:
> +
> +- compatible (mandatory)
> +
> +    Must always include the compatiblity string: "xen,cpupool".
> +
> +- cpupool-cpus (mandatory)
> +
> +    Must be a list of device tree phandle to nodes describing cpus (e.g. 
> having
> +    device_type = "cpu"), it can't be empty.
> +
> +- cpupool-sched (optional)
> +
> +    Must be a string having the name of a Xen scheduler. Check the 
> sched=<...>
> +    boot argument for allowed values [1]. When this property is omitted, the 
> Xen
> +    default scheduler will be used.
> +
> +
> +Constraints
> +===========
> +
> +If no cpupools are specified, all cpus will be assigned to one cpupool
> +implicitly created (Pool-0).
> +
> +If cpupools node are specified, but not every cpu brought up by Xen is 
> assigned,
> +all the not assigned cpu will be assigned to an additional cpupool.
> +
> +If a cpu is assigned to a cpupool, but it's not brought up correctly, Xen 
> will
> +stop.
> +
> +The boot cpu must be assigned to Pool-0, so the cpupool containing that core
> +will become Pool-0 automatically.
> +
> +
> +Examples
> +========
> +
> +A system having two types of core, the following device tree specification 
> will
> +instruct Xen to have two cpupools:
> +
> +- The cpupool with id 0 will have 4 cpus assigned.
> +- The cpupool with id 1 will have 2 cpus assigned.
> +
> +The following example can work only if hmp-unsafe=1 is passed to Xen boot
> +arguments, otherwise not all cores will be brought up by Xen and the cpupool
> +creation process will stop Xen.
> +
> +
> +a72_1: cpu@0 {
> +        compatible = "arm,cortex-a72";
> +        reg = <0x0 0x0>;
> +        device_type = "cpu";
> +        [...]
> +};
> +
> +a72_2: cpu@1 {
> +        compatible = "arm,cortex-a72";
> +        reg = <0x0 0x1>;
> +        device_type = "cpu";
> +        [...]
> +};
> +
> +a53_1: cpu@100 {
> +        compatible = "arm,cortex-a53";
> +        reg = <0x0 0x100>;
> +        device_type = "cpu";
> +        [...]
> +};
> +
> +a53_2: cpu@101 {
> +        compatible = "arm,cortex-a53";
> +        reg = <0x0 0x101>;
> +        device_type = "cpu";
> +        [...]
> +};
> +
> +a53_3: cpu@102 {
> +        compatible = "arm,cortex-a53";
> +        reg = <0x0 0x102>;
> +        device_type = "cpu";
> +        [...]
> +};
> +
> +a53_4: cpu@103 {
> +        compatible = "arm,cortex-a53";
> +        reg = <0x0 0x103>;
> +        device_type = "cpu";
> +        [...]
> +};
> +
> +chosen {
> +
> +    cpupool_a {
> +        compatible = "xen,cpupool";
> +        cpupool-cpus = <&a53_1 &a53_2 &a53_3 &a53_4>;
> +    };
> +    cpupool_b {
> +        compatible = "xen,cpupool";
> +        cpupool-cpus = <&a72_1 &a72_2>;
> +        cpupool-sched = "credit2";
> +    };
> +
> +    [...]
> +
> +};
> +
> +
> +A system having the cpupools specification below will instruct Xen to have 
> three
> +cpupools:
> +
> +- The cpupool Pool-0 will have 2 cpus assigned.
> +- The cpupool Pool-1 will have 2 cpus assigned.
> +- The cpupool Pool-2 will have 2 cpus assigned (created by Xen with all the 
> not
> +  assigned cpus a53_3 and a53_4).
> +
> +chosen {
> +
> +    cpupool_a {
> +        compatible = "xen,cpupool";
> +        cpupool-cpus = <&a53_1 &a53_2>;
> +    };
> +    cpupool_b {
> +        compatible = "xen,cpupool";
> +        cpupool-cpus = <&a72_1 &a72_2>;
> +        cpupool-sched = "null";
> +    };
> +
> +    [...]
> +
> +};
> +
> +[1] docs/misc/xen-command-line.pandoc
> diff --git a/xen/arch/arm/include/asm/smp.h b/xen/arch/arm/include/asm/smp.h
> index af5a2fe65266..83c0cd69767b 100644
> --- a/xen/arch/arm/include/asm/smp.h
> +++ b/xen/arch/arm/include/asm/smp.h
> @@ -34,6 +34,9 @@ extern void init_secondary(void);
>  extern void smp_init_cpus(void);
>  extern void smp_clear_cpu_maps (void);
>  extern int smp_get_max_cpus (void);
> +
> +#define cpu_physical_id(cpu) cpu_logical_map(cpu)
> +
>  #endif
>  
>  /*
> diff --git a/xen/common/Kconfig b/xen/common/Kconfig
> index d921c74d615e..70aac5220e75 100644
> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -22,6 +22,13 @@ config GRANT_TABLE
>  
>         If unsure, say Y.
>  
> +config BOOT_TIME_CPUPOOLS
> +     bool "Create cpupools at boot time"
> +     depends on HAS_DEVICE_TREE
> +     help
> +       Creates cpupools during boot time and assigns cpus to them. Cpupools
> +       options can be specified in the device tree.
> +
>  config ALTERNATIVE_CALL
>       bool
>  
> diff --git a/xen/common/Makefile b/xen/common/Makefile
> index b1e076c30b81..218174ca8b6b 100644
> --- a/xen/common/Makefile
> +++ b/xen/common/Makefile
> @@ -1,5 +1,6 @@
>  obj-$(CONFIG_ARGO) += argo.o
>  obj-y += bitmap.o
> +obj-$(CONFIG_BOOT_TIME_CPUPOOLS) += boot_cpupools.init.o
>  obj-$(CONFIG_HYPFS_CONFIG) += config_data.o
>  obj-$(CONFIG_CORE_PARKING) += core_parking.o
>  obj-y += cpu.o
> diff --git a/xen/common/boot_cpupools.c b/xen/common/boot_cpupools.c
> new file mode 100644
> index 000000000000..9429a5025fc4
> --- /dev/null
> +++ b/xen/common/boot_cpupools.c
> @@ -0,0 +1,207 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * xen/common/boot_cpupools.c
> + *
> + * Code to create cpupools at boot time.
> + *
> + * Copyright (C) 2022 Arm Ltd.
> + */
> +
> +#include <xen/sched.h>
> +#include <asm/acpi.h>
> +
> +/*
> + * pool_cpu_map:   Index is logical cpu number, content is cpupool id, (-1) 
> for
> + *                 unassigned.
> + * pool_sched_map: Index is cpupool id, content is scheduler id, (-1) for
> + *                 unassigned.
> + */
> +static int __initdata pool_cpu_map[NR_CPUS]   = { [0 ... NR_CPUS-1] = -1 };
> +static int __initdata pool_sched_map[NR_CPUS] = { [0 ... NR_CPUS-1] = -1 };
> +static unsigned int __initdata next_pool_id;
> +
> +#define BTCPUPOOLS_DT_NODE_NO_REG     (-1)
> +#define BTCPUPOOLS_DT_NODE_NO_LOG_CPU (-2)
> +
> +static int __init get_logical_cpu_from_hw_id(unsigned int hwid)
> +{
> +    unsigned int i;
> +
> +    for ( i = 0; i < nr_cpu_ids; i++ )
> +    {
> +        if ( cpu_physical_id(i) == hwid )
> +            return i;
> +    }
> +
> +    return -1;
> +}
> +
> +static int __init
> +get_logical_cpu_from_cpu_node(const struct dt_device_node *cpu_node)
> +{
> +    int cpu_num;
> +    const __be32 *prop;
> +    unsigned int cpu_reg;
> +
> +    prop = dt_get_property(cpu_node, "reg", NULL);
> +    if ( !prop )
> +        return BTCPUPOOLS_DT_NODE_NO_REG;
> +
> +    cpu_reg = dt_read_number(prop, dt_n_addr_cells(cpu_node));
> +
> +    cpu_num = get_logical_cpu_from_hw_id(cpu_reg);
> +    if ( cpu_num < 0 )
> +        return BTCPUPOOLS_DT_NODE_NO_LOG_CPU;
> +
> +    return cpu_num;
> +}
> +
> +static int __init check_and_get_sched_id(const char* scheduler_name)
> +{
> +    int sched_id = sched_get_id_by_name(scheduler_name);
> +
> +    if ( sched_id < 0 )
> +        panic("Scheduler %s does not exists!\n", scheduler_name);
> +
> +    return sched_id;
> +}
> +
> +void __init btcpupools_dtb_parse(void)
> +{
> +    const struct dt_device_node *chosen, *node;
> +
> +    if ( !acpi_disabled )
> +        return;
> +
> +    chosen = dt_find_node_by_path("/chosen");
> +    if ( !chosen )
> +        panic("/chosen missing. Boot time cpupools can't be parsed from 
> DT.\n");
> +
> +    dt_for_each_child_node(chosen, node)
> +    {
> +        const struct dt_device_node *phandle_node;
> +        int sched_id = -1;
> +        const char* scheduler_name;
> +        unsigned int i = 0;
> +
> +        if ( !dt_device_is_compatible(node, "xen,cpupool") )
> +            continue;
> +
> +        if ( !dt_property_read_string(node, "cpupool-sched", 
> &scheduler_name) )
> +            sched_id = check_and_get_sched_id(scheduler_name);
> +
> +        phandle_node = dt_parse_phandle(node, "cpupool-cpus", i++);
> +        if ( !phandle_node )
> +            panic("Missing or empty cpupool-cpus property!\n");
> +
> +        while ( phandle_node )
> +        {
> +            int cpu_num;
> +
> +            cpu_num = get_logical_cpu_from_cpu_node(phandle_node);
> +
> +            if ( cpu_num < 0 )
> +                panic("Error retrieving logical cpu from node %s (%d)\n",
> +                      dt_node_name(node), cpu_num);
> +
> +            if ( pool_cpu_map[cpu_num] != -1 )
> +                panic("Logical cpu %d already added to a cpupool!\n", 
> cpu_num);
> +
> +            pool_cpu_map[cpu_num] = next_pool_id;
> +
> +            phandle_node = dt_parse_phandle(node, "cpupool-cpus", i++);
> +        }
> +
> +        /* Save scheduler choice for this cpupool id */
> +        pool_sched_map[next_pool_id] = sched_id;
> +
> +        /* Let Xen generate pool ids */
> +        next_pool_id++;
> +    }
> +}
> +
> +void __init btcpupools_allocate_pools(void)
> +{
> +    unsigned int i;
> +    bool add_extra_cpupool = false;
> +    int swap_id = -1;
> +
> +    /*
> +     * If there are no cpupools, the value of next_pool_id is zero, so the 
> code
> +     * below will assign every cpu to cpupool0 as the default behavior.
> +     * When there are cpupools, the code below is assigning all the not
> +     * assigned cpu to a new pool (next_pool_id value is the last id + 1).
> +     * In the same loop we check if there is any assigned cpu that is not
> +     * online.
> +     */
> +    for ( i = 0; i < nr_cpu_ids; i++ )
> +    {
> +        if ( cpumask_test_cpu(i, &cpu_online_map) )
> +        {
> +            /* Unassigned cpu gets next_pool_id pool id value */
> +            if ( pool_cpu_map[i] < 0 )
> +            {
> +                pool_cpu_map[i] = next_pool_id;
> +                add_extra_cpupool = true;
> +            }
> +
> +            /*
> +             * Cpu0 must be in cpupool0, otherwise some operations like 
> moving
> +             * cpus between cpupools, cpu hotplug, destroying cpupools, 
> shutdown
> +             * of the host, might not work in a sane way.
> +             */
> +            if ( !i && (pool_cpu_map[0] != 0) )
> +                swap_id = pool_cpu_map[0];
> +
> +            if ( swap_id != -1 )
> +            {
> +                if ( pool_cpu_map[i] == swap_id )
> +                    pool_cpu_map[i] = 0;
> +                else if ( pool_cpu_map[i] == 0 )
> +                    pool_cpu_map[i] = swap_id;
> +            }
> +        }
> +        else
> +        {
> +            if ( pool_cpu_map[i] >= 0 )
> +                panic("Pool-%d contains cpu%u that is not online!\n",
> +                      pool_cpu_map[i], i);
> +        }
> +    }
> +
> +    /* A swap happened, swap schedulers between cpupool id 0 and the other */
> +    if ( swap_id != -1 )
> +    {
> +        int swap_sched = pool_sched_map[swap_id];
> +
> +        pool_sched_map[swap_id] = pool_sched_map[0];
> +        pool_sched_map[0] = swap_sched;
> +    }
> +
> +    if ( add_extra_cpupool )
> +        next_pool_id++;
> +
> +    /* Create cpupools with selected schedulers */
> +    for ( i = 0; i < next_pool_id; i++ )
> +        cpupool_create_pool(i, pool_sched_map[i]);
> +}
> +
> +unsigned int __init btcpupools_get_cpupool_id(unsigned int cpu)
> +{
> +    ASSERT((cpu < NR_CPUS) && (pool_cpu_map[cpu] >= 0));
> +
> +    printk(XENLOG_INFO "Logical CPU %u in Pool-%d (Scheduler id: %d).\n",
> +           cpu, pool_cpu_map[cpu], pool_sched_map[pool_cpu_map[cpu]]);
> +
> +    return pool_cpu_map[cpu];
> +}
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * tab-width: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/xen/common/sched/cpupool.c b/xen/common/sched/cpupool.c
> index 89a891af7076..86a175f99cd5 100644
> --- a/xen/common/sched/cpupool.c
> +++ b/xen/common/sched/cpupool.c
> @@ -1247,12 +1247,22 @@ static int __init cf_check cpupool_init(void)
>      cpupool_put(cpupool0);
>      register_cpu_notifier(&cpu_nfb);
>  
> +    btcpupools_dtb_parse();
> +
> +    btcpupools_allocate_pools();
> +
>      spin_lock(&cpupool_lock);
>  
>      cpumask_copy(&cpupool_free_cpus, &cpu_online_map);
>  
>      for_each_cpu ( cpu, &cpupool_free_cpus )
> -        cpupool_assign_cpu_locked(cpupool0, cpu);
> +    {
> +        unsigned int pool_id = btcpupools_get_cpupool_id(cpu);
> +        struct cpupool *pool = cpupool_find_by_id(pool_id);
> +
> +        ASSERT(pool);
> +        cpupool_assign_cpu_locked(pool, cpu);
> +    }
>  
>      spin_unlock(&cpupool_lock);
>  
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index b527f141a1d3..453e98f1cba8 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -1178,6 +1178,20 @@ extern void cf_check dump_runq(unsigned char key);
>  
>  void arch_do_physinfo(struct xen_sysctl_physinfo *pi);
>  
> +#ifdef CONFIG_BOOT_TIME_CPUPOOLS
> +void btcpupools_allocate_pools(void);
> +unsigned int btcpupools_get_cpupool_id(unsigned int cpu);
> +void btcpupools_dtb_parse(void);
> +
> +#else /* !CONFIG_BOOT_TIME_CPUPOOLS */
> +static inline void btcpupools_allocate_pools(void) {}
> +static inline void btcpupools_dtb_parse(void) {}
> +static inline unsigned int btcpupools_get_cpupool_id(unsigned int cpu)
> +{
> +    return 0;
> +}
> +#endif
> +
>  #endif /* __SCHED_H__ */
>  
>  /*
> -- 
> 2.17.1
> 



 


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