On 2024/12/24 0:33, Jonathan Cameron wrote:
> On Fri, 20 Dec 2024 15:53:11 +0800
> Yicong Yang <yangyic...@huawei.com> wrote:
>
>> From: Yicong Yang <yangyic...@hisilicon.com>
>>
>> On building the topology from the devicetree, we've already
>> gotten the SMT thread number of each core. Update the largest
>> SMT thread number and enable the SMT control by the end of
>> topology parsing.
>>
>> The core's SMT control provides two interface to the users [1]:
>> 1) enable/disable SMT by writing on/off
>> 2) enable/disable SMT by writing thread number 1/max_thread_number
>>
>> If a system have more than one SMT thread number the 2) may
>> not handle it well, since there're multiple thread numbers in the
>> system and 2) only accept 1/max_thread_number. So issue a warning
>> to notify the users if such system detected.
>>
>> [1]
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-devices-system-cpu#n542
>> Signed-off-by: Yicong Yang <yangyic...@hisilicon.com>
> Hi Yicong,
>
> Apologies that I'm late to the game on this one.
>
> A few comments inline. Only important one is whether to bail out early
> on error from parse_cluster()
>
thanks for the comments.
> Thanks,
>
> Jonathan
>
>
>> ---
>> drivers/base/arch_topology.c | 26 ++++++++++++++++++++++++++
>> 1 file changed, 26 insertions(+)
>>
>> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
>> index 3ebe77566788..9e81060144c7 100644
>> --- a/drivers/base/arch_topology.c
>> +++ b/drivers/base/arch_topology.c
>> @@ -11,6 +11,7 @@
>> #include <linux/cleanup.h>
>> #include <linux/cpu.h>
>> #include <linux/cpufreq.h>
>> +#include <linux/cpu_smt.h>
>> #include <linux/device.h>
>> #include <linux/of.h>
>> #include <linux/slab.h>
>> @@ -506,6 +507,10 @@ core_initcall(free_raw_capacity);
>> #endif
>>
>> #if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
>> +
>> +/* Maximum SMT thread number detected used to enable the SMT control */
>> +static unsigned int max_smt_thread_num;
>> +
>> /*
>> * This function returns the logic cpu number of the node.
>> * There are basically three kinds of return values:
>> @@ -565,6 +570,17 @@ static int __init parse_core(struct device_node *core,
>> int package_id,
>> i++;
>> } while (1);
>>
>> + /*
>> + * If max_smt_thread_num has been initialized and doesn't match
>> + * the thread number of this entry, then the system has
>> + * heterogeneous SMT topology.
>> + */
>> + if (max_smt_thread_num && max_smt_thread_num != i)
>> + pr_warn_once("Heterogeneous SMT topology is partly supported by
>> SMT control\n");
>> +
>> + if (max_smt_thread_num < i)
>> + max_smt_thread_num = i;
>
> Maybe more self documenting if you use min()? I'm not sure...
> max_smt_thread_num = min(max_smt_thread_num, i);
>
sure, will use max_t here (since we'd like to know the maximum thread number).
>
>> +
>> cpu = get_cpu_for_node(core);
>> if (cpu >= 0) {
>> if (!leaf) {
>> @@ -677,6 +693,16 @@ static int __init parse_socket(struct device_node
>> *socket)
>> if (!has_socket)
>> ret = parse_cluster(socket, 0, -1, 0);
>
> Is it appropriate to check ret before setting num threads?
> if (!has_socket) {
> ret = parse_cluster(socket, 0, -1, 0);
> if (ret)
> return ret;
> }
> ...
>
> return 0;
>
thanks for catching this. since we always need to notify the framework of
the SMT thread number if HOTPLUG_SMT selected, we should make it to 1 if
topology parsing failed. Since on failure the topology information will
be reset, a thread_number of 1 will be handled as SMT not supported.
>>
>> + /*
>> + * Notify the CPU framework of the SMT support. Initialize the
>> + * max_smt_thread_num to 1 if no SMT support detected. A thread
>> + * number of 1 can be handled by the framework so we don't need
>> + * to check max_smt_thread_num to see we support SMT or not.
>> + */
>> + if (!max_smt_thread_num)
>> + max_smt_thread_num = 1;
>> +
>> + cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num);
>
> Trivial but I'd put a blank line here.
>
ok.
Thanks.
