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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2 4/6] xen/cpupool: Create different cpupools at boot time
On Thu, 10 Mar 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.
>
> 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).
This is *a lot* better.
The device tree part is nice. I have only one question left on it: why
do we need a separate scheduler node? Could the "cpupool-sched" property
be a simple string with the scheduler name?
E.g.:
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";
};
To me, it doesn't look like these new "scheduler specification nodes"
bring any benefits. I would just get rid of them.
> +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.
> + *
> + * Copyright (C) 2022 Arm Ltd.
> + */
> +
> +#include <xen/sched.h>
> +
> +#define BTCPUPOOLS_DT_NODE_NO_REG (-1)
> +#define BTCPUPOOLS_DT_NODE_NO_LOG_CPU (-2)
> +
> +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
> +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));
> + }
it doesn't look like the "xen,scheduler" nodes are very useful from a dt
parsing perspective either
> + 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)
> +{
> + 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
Please add { }
> + 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 )
Is that even possible on x86 given that btcpupools_dtb_parse cannot even
run on x86?
If it is not possible, I would remove the code below and simply panic
instead.
> + {
> + /* 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++ )
Please add { }
But actually, the double loop seems a bit excessive for this. Could we
just have a single loop to cpupool_create_pool from 0 to next_pool_id?
We could get rid of pool_cpu_map[i].pool and just rely on
pool_cpu_map[i].pool_id. No need to update pool_cpu_map[i].pool if we
get rid of it: it doesn't look like it is very useful anyway?
> + 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);
> + }
> +}
> +
> +struct cpupool *__init btcpupools_get_cpupool(unsigned int cpu)
> +{
> + return pool_cpu_map[cpu].pool;
> +}
> +
> +/*
> + * 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..b2495ad6d03e 100644
> --- a/xen/common/sched/cpupool.c
> +++ b/xen/common/sched/cpupool.c
> @@ -1247,12 +1247,16 @@ static int __init cf_check cpupool_init(void)
> cpupool_put(cpupool0);
> register_cpu_notifier(&cpu_nfb);
>
> + btcpupools_dtb_parse();
> +
> + btcpupools_allocate_pools(&cpu_online_map);
> +
> 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);
> + cpupool_assign_cpu_locked(btcpupools_get_cpupool(cpu), cpu);
>
> spin_unlock(&cpupool_lock);
>
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index 2c10303f0187..de4e8feea399 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -1176,6 +1176,25 @@ 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(const cpumask_t *cpu_online_map);
> +struct cpupool *btcpupools_get_cpupool(unsigned int cpu);
> +
> +#ifdef CONFIG_ARM
> +void btcpupools_dtb_parse(void);
> +#else
> +static inline void btcpupools_dtb_parse(void) {}
> +#endif
> +
> +#else
> +static inline void btcpupools_allocate_pools(const cpumask_t
> *cpu_online_map) {}
> +static inline void btcpupools_dtb_parse(void) {}
> +static inline struct cpupool *btcpupools_get_cpupool(unsigned int cpu)
> +{
> + return cpupool0;
> +}
> +#endif
> +
> #endif /* __SCHED_H__ */
>
> /*
> --
> 2.17.1
>
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