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From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
To: "thomas@monjalon.net" <thomas@monjalon.net>,
	Stephen Hemminger <stephen@networkplumber.org>
Cc: "dev@dpdk.org" <dev@dpdk.org>, Joyce Kong <Joyce.Kong@arm.com>,
	"konstantin.ananyev@intel.com" <konstantin.ananyev@intel.com>,
	nd <nd@arm.com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH v2] eal/rwlock: add note about writer starvation
Date: Fri, 12 Feb 2021 00:21:19 +0000
Message-ID: <DBAPR08MB5814224330DD6E75F964B6AE988B9@DBAPR08MB5814.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <6427760.fPJ3V7j96H@thomas>

<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
> 


  reply	other threads:[~2021-02-12  0:21 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-08 19:13 [dpdk-dev] Reader-Writer lock starvation issues Stephen Hemminger
2021-01-08 21:27 ` Honnappa Nagarahalli
2021-01-11 11:52   ` Ferruh Yigit
2021-01-11 13:05     ` Honnappa Nagarahalli
2021-01-12  1:04 ` [dpdk-dev] [PATCH] eal/rwlock: add note about writer starvation Stephen Hemminger
2021-01-14 16:55   ` [dpdk-dev] [PATCH v2] " Stephen Hemminger
2021-02-11 22:51     ` Thomas Monjalon
2021-02-12  0:21       ` Honnappa Nagarahalli [this message]
2021-05-12 19:10         ` Thomas Monjalon

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