[PATCH v6] eal: add seqlock

[Stephen Hemminger]

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.