From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
To: "Zhang, Qi Z" <qi.z.zhang@intel.com>,
Lance Richardson <lance.richardson@broadcom.com>
Cc: Joyce Kong <Joyce.Kong@arm.com>,
"Xing, Beilei" <beilei.xing@intel.com>,
Ruifeng Wang <Ruifeng.Wang@arm.com>,
"Richardson, Bruce" <bruce.richardson@intel.com>,
"Zhang, Helin" <helin.zhang@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>,
"stable@dpdk.org" <stable@dpdk.org>, nd <nd@arm.com>,
Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
nd <nd@arm.com>
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH v3 2/2] net/i40e: replace SMP barrier with thread fence
Date: Thu, 8 Jul 2021 14:44:51 +0000 [thread overview]
Message-ID: <DBAPR08MB58146AA98BC7DE5311F24ED898199@DBAPR08MB5814.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <478df4d4cc9b472aa4cd158cee0ee0c6@intel.com>
<snip>
> > > >
> > > > Simply replace the SMP barrier with atomic thread fence for i40e
> > > > hw ring
> > sacn,
> > > > if there is no synchronization point.
> > > >
> > > > Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> > > > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > > > ---
> > > > drivers/net/i40e/i40e_rxtx.c | 3 ++-
> > > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/net/i40e/i40e_rxtx.c
> > > > b/drivers/net/i40e/i40e_rxtx.c index 9aaabfd92..86e2f083e 100644
> > > > --- a/drivers/net/i40e/i40e_rxtx.c
> > > > +++ b/drivers/net/i40e/i40e_rxtx.c
> > > > @@ -482,7 +482,8 @@ i40e_rx_scan_hw_ring(struct i40e_rx_queue
> > > > *rxq)
> > > >
> > I40E_RXD_QW1_STATUS_SHIFT;
> > > > }
> > > >
> > > > - rte_smp_rmb();
> > > > + /* This barrier is to order loads of different words
> > > > + in the
> > descriptor */
> > > > + rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
> > >
> > > Now for x86, you actually replace a compiler barrier with a memory
> > > fence,
> > this may have potential performance impact which need additional
> > resource to investigate
> >
> > No memory fence instruction is generated for __ATOMIC_ACQUIRE on x86
> > for any version of gcc or clang that I've tried, based on experiments
> > here:
> >
> > https://godbolt.org/z/Yxr1vGhKP
>
> Nice tool!
> I try to write some dummy code combined with or without
> __atomic_thread_fence(__ATOMIC_ACQUIRE)
> but I didn't see any difference of the generated assembly code, does that means
> __atomic_thread_fence(__ATOMIC_ACQUIRE) just does nothing on x86?
Yes, it should not have any barriers generated for x86. At the same time it also acts as a compiler barrier.
next prev parent reply other threads:[~2021-07-08 14:45 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210604073405.14880-1-joyce.kong@arm.com>
2021-06-23 8:43 ` [dpdk-stable] [PATCH v2] net/i40e: add logic of processing continuous DD bits for Arm Joyce Kong
2021-06-30 1:14 ` Honnappa Nagarahalli
2021-07-05 3:41 ` Joyce Kong
2021-07-06 6:54 ` [dpdk-stable] [PATCH v3 0/2] fixes for i40e hw scan ring Joyce Kong
2021-07-06 6:54 ` [dpdk-stable] [PATCH v3 1/2] net/i40e: add logic of processing continuous DD bits for Arm Joyce Kong
2021-07-09 3:05 ` Zhang, Qi Z
2021-07-06 6:54 ` [dpdk-stable] [PATCH v3 2/2] net/i40e: replace SMP barrier with thread fence Joyce Kong
2021-07-08 12:09 ` Zhang, Qi Z
2021-07-08 13:51 ` [dpdk-stable] [dpdk-dev] " Lance Richardson
2021-07-08 14:26 ` Zhang, Qi Z
2021-07-08 14:44 ` Honnappa Nagarahalli [this message]
2021-07-13 0:46 ` [dpdk-stable] " Zhang, Qi Z
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