[haiku-development] Re: RFC: Removing B_MAX_CPU_NUM and reworking system_info
- From: Pawel Dziepak <pdziepak@xxxxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Tue, 3 Dec 2013 20:46:42 +0100
2013/12/2 Ingo Weinhold <ingo_weinhold@xxxxxx>:
> On 12/01/2013 10:00 PM, Pawel Dziepak wrote:
>> typedef struct {
>> bigtime_t active_time;
>> } cpu_statistics;
>
>
> Topology and current state info could be added. If easily available, the
> current load factor as well.
The problem with the topology is that we really don't want to
introduce any bound on number of topology levels. Perhaps, a separate
function like that would be a better solution:
status_t get_cpu_topology_ids(uint32 cpu, uint32* topologyIDs, uint32*
topologyLevelCount);
Where topologyIDs is an array of CPU IDs at each level (starting from
SMT), if the ID of two logical CPUs are equal at a certain level then
these processors belong to the same unit this level represent. Also,
something similar could be done to present cache information (i.e.
size of a cache at each level and which CPUs share a given level of
cache). Actually, if the application knew the initial APIC ID it would
be able to obtain this information without the kernel's help. However,
since a syscall is necessary to map processor IDs used by the system
to a initial IDs, the kernel could as well present all topology
information, especially, since it is a bit tricky to get from CPU and
the kernel already has it processed and ready.
>> #define get_system_statistics(stat) _get_system_statistics(stat,
>> sizeof(*stat))
>>
>> status_t _get_system_statistics(system_statistics* stat, size_t size);
>>
>> #define get_cpu_statistics(firstCPU, cpuCount, stat)
>> _get_cpu_statistics(firstCPU, cpuCount, stat, sizeof(*stat))
>>
>> status_t _get_system_statistics(int32 firstCPU, int32 cpuCount,
>> cpu_statistics* stat, size_t elementSize);
>>
>> system_statistics is basically current system_info with both
>> problematic and obsolete fileds removed. get_cpu_statistics() allow to
>> obtain statistics of several logical processors using just one system
>> call. Macros ensure that both system_statistics and cpu_statistics can
>> be extended without breaking ABI (_get_cpu_statistics() expects stat
>> to point to a buffer of size cpuCount * elementSize).
>
>
> The macros won't be necessary. The same can be achieved with ELF symbol
> versioning (also allowing reordering of fields). In fact we wouldn't even
> need to introduce new structure/function names, but could just continue to
> use system_info/cpu_info/get_system_info(). The advantage is that in many
> use cases of get_system_info() the code wouldn't even need to be adjusted
> (the change of signedness of most fields may cause some warnings, though).
I haven't thought about that. That would keep things neater.
I don't think the change of signedness would cause much trouble. The
only field that an application may compare against while iterating is
cpu_count, but any code using that has to be changed anyway due to the
removal of system_info::cpu_infos.
Paweł
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