Re: [PATCH v2 4/6] xen/cpupool: Create different cpupools at boot time

[Juergen Gross <jgross@xxxxxxxx>]

On 10.03.22 18:10, 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.
>
> Documentation is created to explain the feature.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
> 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 | 156 ++++++++++++++++++
>   xen/common/Kconfig                     |   8 +
>   xen/common/Makefile                    |   1 +
>   xen/common/boot_cpupools.c             | 212 +++++++++++++++++++++++++
>   xen/common/sched/cpupool.c             |   6 +-
>   xen/include/xen/sched.h                |  19 +++
>   6 files changed, 401 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..d5a82ed0d45a
> --- /dev/null
> +++ b/docs/misc/arm/device-tree/cpupools.txt
> @@ -0,0 +1,156 @@
> +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.
> +
> +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 device tree phandle to a node having "xen,scheduler" compatible
> +    (description below), it has no effect when the cpupool refers to the 
> cpupool
> +    number zero, in that case the default Xen scheduler is selected 
> (sched=<...>
> +    boot argument).
> +
> +
> +A scheduler specification node is a device tree node that contains the 
> following
> +properties:
> +
> +- compatible (mandatory)
> +
> +    Must always include the compatiblity string: "xen,scheduler".
> +
> +- sched-name (mandatory)
> +
> +    Must be a string having the name of a Xen scheduler, check the sched=<...>
> +    boot argument for allowed values.
> +
> +
> +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.
> +
> +
> +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 {
> +
> +    sched: sched_a {
> +        compatible = "xen,scheduler";
> +        sched-name = "credit2";
> +    };
> +    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 = <&sched>;
> +    };
> +
> +    [...]
> +
> +};
> +
> +
> +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 {
> +
> +    sched: sched_a {
> +        compatible = "xen,scheduler";
> +        sched-name = "null";
> +    };
> +    cpupool_a {
> +        compatible = "xen,cpupool";
> +        cpupool-cpus = <&a53_1 &a53_2>;
> +    };
> +    cpupool_b {
> +        compatible = "xen,cpupool";
> +        cpupool-cpus = <&a72_1 &a72_2>;
> +        cpupool-sched = <&sched>;
> +    };
> +
> +    [...]
> +
> +};
> \ No newline at end of file
> diff --git a/xen/common/Kconfig b/xen/common/Kconfig
> index 64439438891c..dc9eed31682f 100644
> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -22,6 +22,14 @@ config GRANT_TABLE
>   
>   	  If unsure, say Y.
>   
> +config BOOT_TIME_CPUPOOLS
> +       bool "Create cpupools at boot time"
> +       depends on HAS_DEVICE_TREE
> +       default n
> +       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 dc8d3a13f5b8..c5949785ab28 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.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..e8529a902d21
> --- /dev/null
> +++ b/xen/common/boot_cpupools.c
> @@ -0,0 +1,212 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * xen/common/boot_cpupools.c
> + *
> + * Code to create cpupools at boot time for arm architecture.
Please drop the arm reference here.

> + *
> + * Copyright (C) 2022 Arm Ltd.
> + */
> +
> +#include <xen/sched.h>
> +
> +#define BTCPUPOOLS_DT_NODE_NO_REG     (-1)
> +#define BTCPUPOOLS_DT_NODE_NO_LOG_CPU (-2)
Move those inside the #ifdef below, please

> +
> +struct pool_map {
> +    int pool_id;
> +    int sched_id;
> +    struct cpupool *pool;
> +};
> +
> +static struct pool_map __initdata pool_cpu_map[NR_CPUS] =
> +    { [0 ... NR_CPUS-1] = {.pool_id = -1, .sched_id = -1, .pool = NULL} };
> +static unsigned int __initdata next_pool_id;
> +
> +#ifdef CONFIG_ARM
Shouldn't this be CONFIG_HAS_DEVICE_TREE?

> +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_logical_map(i) == hwid )
> +            return i;
> +
> +    return -1;
> +}
> +
> +static int __init
> +get_logical_cpu_from_cpu_node(const struct dt_device_node *cpu_node)
> +{
> +    unsigned int cpu_reg, cpu_num;
> +    const __be32 *prop;
> +
> +    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;
> +
> +    chosen = dt_find_node_by_path("/chosen");
> +    if ( !chosen )
> +        return;
> +
> +    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;
> +
> +        phandle_node = dt_parse_phandle(node, "cpupool-sched", 0);
> +        if ( phandle_node )
> +        {
> +            if ( !dt_device_is_compatible(phandle_node, "xen,scheduler") )
> +                panic("cpupool-sched must be a xen,scheduler compatible"
> +                      "node!\n");
> +            if ( !dt_property_read_string(phandle_node, "sched-name",
> +                                          &scheduler_name) )
> +                sched_id = check_and_get_sched_id(scheduler_name);
> +            else
> +                panic("Error trying to read sched-name in %s!\n",
> +                      dt_node_name(phandle_node));
> +        }
> +
> +        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].pool_id != -1 )
> +                panic("Logical cpu %d already added to a cpupool!\n", cpu_num);
> +
> +            pool_cpu_map[cpu_num].pool_id = next_pool_id;
> +            pool_cpu_map[cpu_num].sched_id = sched_id;
> +
> +            phandle_node = dt_parse_phandle(node, "cpupool-cpus", i++);
> +        }
> +
> +        /* Let Xen generate pool ids */
> +        next_pool_id++;
> +    }
> +}
> +#endif
> +
> +void __init btcpupools_allocate_pools(const cpumask_t *cpu_online_map)
Either rename the parameter or drop it completely.

Right now shadowing cpu_online_map is no real problem, because the only
caller is passing the global cpu_online_map, but in case another caller
with different needs would come up, this would be rather confusing.

With the x86 specific loop in this function I don't see how a different
map than the global cpu_online_map could work, so I think dropping the
parameter is the best move.

> +{
> +    unsigned int cpu_num;
> +
> +    /*
> +     * 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 ( cpu_num = 0; cpu_num < nr_cpu_ids; cpu_num++ )
> +        if ( cpumask_test_cpu(cpu_num, cpu_online_map) )
> +        {
> +            if ( pool_cpu_map[cpu_num].pool_id < 0 )
> +                pool_cpu_map[cpu_num].pool_id = next_pool_id;
> +        }
> +        else
> +            if ( pool_cpu_map[cpu_num].pool_id >= 0 )
> +                panic("Pool-%d contains cpu%u that is not online!\n",
> +                      pool_cpu_map[cpu_num].pool_id, cpu_num);
> +
> +#ifdef CONFIG_X86
> +    /* Cpu0 must be in cpupool0 for x86 */
> +    if ( pool_cpu_map[0].pool_id != 0 )
> +    {
> +        /* The cpupool containing cpu0 will become cpupool0 */
> +        unsigned int swap_id = pool_cpu_map[0].pool_id;
> +        for_each_cpu ( cpu_num, cpu_online_map )
> +            if ( pool_cpu_map[cpu_num].pool_id == swap_id )
> +                pool_cpu_map[cpu_num].pool_id = 0;
> +            else if ( pool_cpu_map[cpu_num].pool_id == 0 )
> +                pool_cpu_map[cpu_num].pool_id = swap_id;
> +    }
> +#endif
> +
> +    for_each_cpu ( cpu_num, cpu_online_map )
> +    {
> +        struct cpupool *pool = NULL;
> +        int pool_id, sched_id;
> +
> +        pool_id = pool_cpu_map[cpu_num].pool_id;
> +        sched_id = pool_cpu_map[cpu_num].sched_id;
> +
> +        if ( pool_id )
> +        {
> +            unsigned int i;
> +
> +            /* Look for previously created pool with id pool_id */
> +            for ( i = 0; i < cpu_num; i++ )
> +                if ( (pool_cpu_map[i].pool_id == pool_id) &&
> +                     pool_cpu_map[i].pool )
> +                {
> +                    pool = pool_cpu_map[i].pool;
> +                    break;
> +                }
> +
> +            /* If no pool was created before, create it */
> +            if ( !pool )
> +                pool = cpupool_create_pool(pool_id, sched_id);
> +            if ( !pool )
> +                panic("Error creating pool id %u!\n", pool_id);
> +        }
> +        else
> +            pool = cpupool0;
> +
> +        pool_cpu_map[cpu_num].pool = pool;
> +        printk(XENLOG_INFO "Logical CPU %u in Pool-%u.\n", cpu_num, pool_id);
> +    }
> +}

Juergen

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