Re: [PATCH 11/17] net/iavf: use previous value atomic fetch operations

From: Tyler Retzlaff <roretzla@linux.microsoft.com>
To: Ruifeng Wang <Ruifeng.Wang@arm.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	"thomas@monjalon.net" <thomas@monjalon.net>, nd <nd@arm.com>
Subject: Re: [PATCH 11/17] net/iavf: use previous value atomic fetch operations
Date: Thu, 2 Mar 2023 07:50:54 -0800	[thread overview]
Message-ID: <20230302155054.GA29061@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> (raw)
In-Reply-To: <AM9PR08MB708580C2D1064156FA7A58759EB29@AM9PR08MB7085.eurprd08.prod.outlook.com>

On Thu, Mar 02, 2023 at 09:28:09AM +0000, Ruifeng Wang wrote:
> > -----Original Message-----
> > From: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > Sent: Thursday, March 2, 2023 8:48 AM
> > To: dev@dpdk.org
> > Cc: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>; thomas@monjalon.net; Tyler
> > Retzlaff <roretzla@linux.microsoft.com>
> > Subject: [PATCH 11/17] net/iavf: use previous value atomic fetch operations
> > 
> > Use __atomic_fetch_{add,and,or,sub,xor} instead of __atomic_{add,and,or,sub,xor}_fetch
> > when we have no interest in the result of the operation.
> > 
> > Reduces unnecessary codegen that provided the result of the atomic operation that was not
> > used.
> > 
> > Change brings closer alignment with atomics available in C11 standard and will reduce
> > review effort when they are integrated.
> > 
> > Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > ---
> >  drivers/net/iavf/iavf_vchnl.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/iavf/iavf_vchnl.c b/drivers/net/iavf/iavf_vchnl.c index
> > 9adaadb..73875d7 100644
> > --- a/drivers/net/iavf/iavf_vchnl.c
> > +++ b/drivers/net/iavf/iavf_vchnl.c
> > @@ -128,7 +128,7 @@ struct iavf_event_handler {
> >  	int err = pipe(handler->fd);
> >  #endif
> >  	if (err != 0) {
> > -		__atomic_sub_fetch(&handler->ndev, 1, __ATOMIC_RELAXED);
> > +		__atomic_fetch_sub(&handler->ndev, 1, __ATOMIC_RELAXED);
> >  		return -1;
> >  	}
> > 
> > @@ -137,7 +137,7 @@ struct iavf_event_handler {
> > 
> >  	if (rte_ctrl_thread_create(&handler->tid, "iavf-event-thread",
> >  				NULL, iavf_dev_event_handle, NULL)) {
> > -		__atomic_sub_fetch(&handler->ndev, 1, __ATOMIC_RELAXED);
> > +		__atomic_fetch_sub(&handler->ndev, 1, __ATOMIC_RELAXED);
> >  		return -1;
> >  	}
> > 
> > @@ -533,7 +533,7 @@ struct iavf_event_handler {
> >  				/* read message and it's expected one */
> >  				if (msg_opc == vf->pend_cmd) {
> >  					uint32_t cmd_count =
> > -					__atomic_sub_fetch(&vf->pend_cmd_count,
> > +					__atomic_fetch_sub(&vf->pend_cmd_count,
> 
> It doesn't apply here. The return value is used.
> The rest of the series looks good to me.

oh, i was blind to the line wrapping. definitely not correct.

thanks for catching this, will submit v2 with it reverted.

> 
> >  							1, __ATOMIC_RELAXED);
> >  					if (cmd_count == 0)
> >  						_notify_cmd(vf, msg_ret);
> > --
> > 1.8.3.1