From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Ilya Maximets <i.maximets@samsung.com>,
Yuanhan Liu <yuanhan.liu@linux.intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"Xie, Huawei" <huawei.xie@intel.com>,
Dyasly Sergey <s.dyasly@samsung.com>
Subject: Re: [dpdk-dev] [PATCH v4] vhost: use SMP barriers instead of compiler ones.
Date: Mon, 21 Mar 2016 14:07:32 +0000 [thread overview]
Message-ID: <2601191342CEEE43887BDE71AB97725836B1F296@irsmsx105.ger.corp.intel.com> (raw)
In-Reply-To: <56EF7D72.1050108@samsung.com>
> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Ilya Maximets
> Sent: Monday, March 21, 2016 4:50 AM
> To: Yuanhan Liu
> Cc: dev@dpdk.org; Xie, Huawei; Dyasly Sergey
> Subject: Re: [dpdk-dev] [PATCH v4] vhost: use SMP barriers instead of compiler ones.
>
>
>
> On 18.03.2016 15:41, Yuanhan Liu wrote:
> > On Fri, Mar 18, 2016 at 03:23:53PM +0300, Ilya Maximets wrote:
> >> Since commit 4c02e453cc62 ("eal: introduce SMP memory barriers") virtio
> >> uses architecture dependent SMP barriers. vHost should use them too.
> >>
> >> Fixes: 4c02e453cc62 ("eal: introduce SMP memory barriers")
> >>
> >> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> >> ---
> >> lib/librte_vhost/vhost_rxtx.c | 7 ++++---
> >> 1 file changed, 4 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
> >> index b4da665..859c669 100644
> >> --- a/lib/librte_vhost/vhost_rxtx.c
> >> +++ b/lib/librte_vhost/vhost_rxtx.c
> >> @@ -315,7 +315,7 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
> >> rte_prefetch0(&vq->desc[desc_indexes[i+1]]);
> >> }
> >>
> >> - rte_compiler_barrier();
> >> + rte_smp_wmb();
> >>
> >> /* Wait until it's our turn to add our buffer to the used ring. */
> >> while (unlikely(vq->last_used_idx != res_start_idx))
> >> @@ -565,7 +565,7 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
> >>
> >> nr_used = copy_mbuf_to_desc_mergeable(dev, vq, start, end,
> >> pkts[pkt_idx]);
> >> - rte_compiler_barrier();
> >> + rte_smp_wmb();
> >>
> >> /*
> >> * Wait until it's our turn to add our buffer
> >> @@ -923,7 +923,8 @@ rte_vhost_dequeue_burst(struct virtio_net *dev, uint16_t queue_id,
> >> sizeof(vq->used->ring[used_idx]));
> >> }
> >>
> >> - rte_compiler_barrier();
> >> + rte_smp_wmb();
> >> + rte_smp_rmb();
> >
> > rte_smp_mb?
>
> rte_smp_mb() is a real mm_fence() on x86. And we don't need to synchronize reads with
> writes here, only reads with reads and writes with writes. It is enough because next
> increment uses read and write. Pair of barriers is better because it will not impact
> on performance on x86.
Not arguing about that particular patch, just a question:
Why do we have:
#define rte_smp_mb() rte_mb()
for x86?
Why not just:
#define rte_smp_mb() rte_compiler_barrier()
here?
I meant for situations when we do need real mfence, there is an 'rte_mb' to use.
Konstantin
>
> Best regards, Ilya Maximets.
next prev parent reply other threads:[~2016-03-21 14:07 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-24 11:47 [dpdk-dev] [PATCH RFC v3 0/3] Thread safe rte_vhost_enqueue_burst() Ilya Maximets
2016-02-24 11:47 ` [dpdk-dev] [PATCH RFC v3 1/3] vhost: use SMP barriers instead of compiler ones Ilya Maximets
2016-03-18 10:08 ` Xie, Huawei
2016-03-18 10:23 ` Ilya Maximets
2016-03-18 10:27 ` Xie, Huawei
2016-03-18 10:39 ` Ilya Maximets
2016-03-18 10:47 ` Xie, Huawei
2016-03-18 11:00 ` Ilya Maximets
[not found] ` <C37D651A908B024F974696C65296B57B4C67825C@SHSMSX101.ccr.corp.intel.com>
[not found] ` <56EBE9AE.9070400@samsung.com>
[not found] ` <56EBF256.8040409@samsung.com>
2016-03-18 12:28 ` Ilya Maximets
2016-03-18 12:23 ` [dpdk-dev] [PATCH v4] " Ilya Maximets
2016-03-18 12:41 ` Yuanhan Liu
2016-03-21 4:49 ` Ilya Maximets
2016-03-21 14:07 ` Ananyev, Konstantin [this message]
2016-03-21 17:25 ` Xie, Huawei
2016-03-21 17:36 ` Ananyev, Konstantin
2016-03-23 14:07 ` Xie, Huawei
2016-03-31 13:46 ` Thomas Monjalon
2016-02-24 11:47 ` [dpdk-dev] [PATCH RFC v3 2/3] vhost: make buf vector for scatter RX local Ilya Maximets
2016-02-24 11:47 ` [dpdk-dev] [PATCH RFC v3 3/3] vhost: avoid reordering of used->idx and last_used_idx updating Ilya Maximets
2016-03-17 15:29 ` [dpdk-dev] [PATCH RFC v3 0/3] Thread safe rte_vhost_enqueue_burst() Thomas Monjalon
2016-03-18 8:00 ` Yuanhan Liu
2016-03-18 8:09 ` Thomas Monjalon
2016-03-18 9:16 ` Yuanhan Liu
2016-03-18 9:34 ` Thomas Monjalon
2016-03-18 9:46 ` Yuanhan Liu
2016-03-18 9:55 ` Ilya Maximets
2016-03-18 10:10 ` Xie, Huawei
2016-03-18 10:24 ` Thomas Monjalon
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