> On 11 Mar 2022, at 14:11, Luca Fancellu <luca.fance...@arm.com> wrote:
>
> 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)
>
I meant a wrapper of this function, since this needs the lock...
> 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
