Re: [dpdk-dev] [PATCH v2] eal/rwlock: add note about writer starvation

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> 
> 14/01/2021 17:55, Stephen Hemminger:
> > The implementation of reader/writer locks in DPDK (from first release)
> > is simple and fast. But it can lead to writer starvation issues.
> >
> > It is not easy to fix this without changing ABI and potentially
> > breaking customer applications that are expect the unfair behavior.
> 
> typo: "are expect"
> 
> > The wikipedia page on reader-writer problem has a similar example
> > which summarizes the problem pretty well.
> 
> Maybe add the URL in the commit message?
> 
> >
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > ---
> > --- a/lib/librte_eal/include/generic/rte_rwlock.h
> > +++ b/lib/librte_eal/include/generic/rte_rwlock.h
> > + * Note: This version of reader/writer locks is not fair because
                                ^^^^^^ may be "implementation" would be better?

> > + * readers do not block for pending writers. A stream of readers can
> > + * subsequently lock out all potential writers and starve them.
> > + * This is because after the first reader locks the resource,
> > + * no writer can lock it. The writer will only be able to get the
> > + lock
> > + * when it will only be released by the last reader.
This looks good. Though the writer starvation is prominent, the reader starvation is possible if there is a stream of writers when a writer holds the lock. Should we call this out too?

> 
> You did not get review, probably because nobody was Cc'ed.
> +Cc Honnappa, Joyce and Konstantin
>