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From: Phil Yang <Phil.Yang@arm.com>
To: "thomas@monjalon.net" <thomas@monjalon.net>
Cc: "erik.g.carrillo@intel.com" <erik.g.carrillo@intel.com>,
	"rsanford@akamai.com" <rsanford@akamai.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"david.marchand@redhat.com" <david.marchand@redhat.com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	Gavin Hu <Gavin.Hu@arm.com>, nd <nd@arm.com>,  nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH v3] lib/timer: relax barrier for status update
Date: Sun, 26 Apr 2020 07:36:07 +0000
Message-ID: <VE1PR08MB4640FC55C1E17147968BA70DE9AE0@VE1PR08MB4640.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <1873559.ZhSLo9btvA@thomas>

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Sunday, April 26, 2020 1:18 AM
> To: Phil Yang <Phil.Yang@arm.com>
> Cc: erik.g.carrillo@intel.com; rsanford@akamai.com; dev@dpdk.org;
> david.marchand@redhat.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Gavin Hu <Gavin.Hu@arm.com>; nd
> <nd@arm.com>
> Subject: Re: [dpdk-dev] [PATCH v3] lib/timer: relax barrier for status update
> 
> 24/04/2020 09:24, Phil Yang:
> > Volatile has no ordering semantics. The rte_timer structure defines
> > timer status as a volatile variable and uses the rte_r/wmb barrier
> > to guarantee inter-thread visibility.
> >
> > This patch optimized the volatile operation with c11 atomic operations
> > and one-way barrier to save the performance penalty. According to the
> > timer_perf_autotest benchmarking results, this patch can uplift 10%~16%
> > timer appending performance, 3%~20% timer resetting performance and
> 45%
> > timer callbacks scheduling performance on aarch64 and no loss in
> > performance for x86.
> >
> > Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > Signed-off-by: Phil Yang <phil.yang@arm.com>
> > Reviewed-by: Gavin Hu <gavin.hu@arm.com>
> > Acked-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
> [...]
> > --- a/lib/librte_timer/rte_timer.h
> > +++ b/lib/librte_timer/rte_timer.h
> > @@ -101,7 +101,7 @@ struct rte_timer
> > -	volatile union rte_timer_status status; /**< Status of timer. */
> > +	union rte_timer_status status; /**< Status of timer. */
> 
> Unfortunately, I cannot merge this patch because it breaks the ABI:
> 
>   [C]'function void rte_timer_init(rte_timer*)' at rte_timer.c:214:1 has some
> indirect sub-type changes:
>     parameter 1 of type 'rte_timer*' has sub-type changes:
>       in pointed to type 'struct rte_timer' at rte_timer.h:100:1:
>         type size hasn't changed
>         1 data member changes (2 filtered):
>          type of 'volatile rte_timer_status rte_timer::status' changed:
>            entity changed from 'volatile rte_timer_status' to 'union
> rte_timer_status' at rte_timer.h:67:1
>            type size hasn't changed
> 

I think we can revert it to the original definition of rte_timer and keep the union rte_timer_status volatile-qualified. 
Because with or without this 'volatile' qualify, it generates the same code on aarch64 and x86.
So it seems acceptable to ignore it to make the ABI compatible?

Thank,
Phil

  reply	other threads:[~2020-04-26  7:36 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-24  6:42 [dpdk-dev] [PATCH 1/2] lib/timer: protect timer subsystem initialized with lock Phil Yang
2020-02-24  6:42 ` [dpdk-dev] [PATCH 2/2] lib/timer: relax barrier for status update Phil Yang
2020-04-08 10:23   ` Phil Yang
2020-04-08 21:10   ` Carrillo, Erik G
2020-04-08 21:16     ` Honnappa Nagarahalli
2020-04-08 21:26       ` Carrillo, Erik G
2020-04-08 21:56         ` Honnappa Nagarahalli
2020-04-09 19:29           ` Carrillo, Erik G
2020-04-10  4:39             ` Phil Yang
2020-04-20 16:05   ` [dpdk-dev] [PATCH v2] " Phil Yang
2020-04-23 20:06     ` Honnappa Nagarahalli
2020-04-24  1:26       ` Carrillo, Erik G
2020-04-24  7:27         ` Phil Yang
2020-04-24  7:24     ` [dpdk-dev] [PATCH v3] " Phil Yang
2020-04-25 17:17       ` Thomas Monjalon
2020-04-26  7:36         ` Phil Yang [this message]
2020-04-26 12:18           ` Carrillo, Erik G
2020-04-26 14:20             ` Phil Yang
2020-04-26 19:30               ` Carrillo, Erik G
2020-04-26 14:45       ` [dpdk-dev] [PATCH v4] " Phil Yang
2020-04-26 20:06         ` Thomas Monjalon
2020-04-25 14:36     ` [dpdk-dev] [PATCH v2] " Thomas Monjalon
2020-04-25 15:51       ` Phil Yang
2020-04-25 16:07         ` Thomas Monjalon
2020-02-25 22:26 ` [dpdk-dev] [PATCH 1/2] lib/timer: protect timer subsystem initialized with lock Carrillo, Erik G
2020-04-25 17:21   ` [dpdk-dev] [dpdk-stable] " Thomas Monjalon

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