Hi Stefano,
> On 11 Mar 2022, at 03:57, Stefano Stabellini <sstabell...@kernel.org> wrote:
>
> 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.fance...@arm.com>
>> ---
>> 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.
From a comment of Juergen on the second patch I thought someone sees the need to
have a way to set scheduling parameters:
“you are allowing to use another scheduler,
but what if someone wants to set non-standard scheduling parameters
(e.g. another time slice)?”
So I thought I could introduce a scheduler specification node that could in the
future be
extended and used to set scheduling parameter.
If it is something that is not needed, I will get rid of it.
>
>
>> +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.
Currently x86 doesn’t have a way to specify cpupools, so for now on x86 there
will
be only cpupool 0 with every cpu attached, I thought I had to handle the case
if in
the future someone adds a way to specify cpupools (cmdline?).
If you think this should be handled only by who implements that feature, I will
remove
completely the block.
>
>
>> + {
>> + /* 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?
Yes we could create all the cpupools in a loop easily, but to retrieve the
pointer
from the cpupool list I would need something, I can make public this function:
static struct cpupool *cpupool_find_by_id(unsigned int poolid)
from cpupool.c to get the pointer from the pool id, do you think it can be ok?
I will address your other findings in the next serie.
Thank you for your review.
Cheers,
Luca
>
>
>> + 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
