[PATCH v6] eal: add seqlock

[Mattias Rönnblom]

On 2022-05-09 05:48, Stephen Hemminger wrote:
> On Sun, 8 May 2022 21:40:58 +0200
> Mattias Rönnblom <hofors at lysator.liu.se> wrote:
> 
>>> I think would be good to have the sequence count (read side only) like
>>> the kernel and sequence lock (sequence count + spinlock) as separate things.
>>>
>>> That way the application could use sequence count + ticket lock if it
>>> needed to scale to more writers.
>>>    
>>
>> Sounds reasonable. Would that be something like:
>>
>> typedef struct {
>> 	uint32_t sn;
>> } rte_seqlock_t;
>>
>> rte_seqlock_read_begin()
>> rte_seqlock_read_retry()
>> rte_seqlock_write_begin()
>> rte_seqlock_write_end()
>>
>> typedef struct {
>> 	rte_seqlock_t seqlock;
>> 	rte_spinlock_t wlock;
>> } rte_<something>_t;
>>
>> rte_<something>_read_begin()
>> rte_<something>_read_retry()
>> rte_<something>_write_lock()
>> rte_<something>_write_unlock()
>>
>> or are you suggesting removing the spinlock altogether, and leave
>> writer-side synchronization to the application (at least in this DPDK
>> release)?
> 
> 
> No, like Linux kernel. Use seqcount for the reader counter only object
> and seqlock for the seqcount + spinlock version.

Should rte_seqcount_t be in a separate file?

Normally, I would use the "header file per 'class'" pattern (unless 
things are very tightly coupled), but I suspect DPDK style is the 
"header file per group of related 'classes'".