> -Original Message-
> From: Xie, Huawei
> Sent: Wednesday, January 28, 2015 12:16 AM
> To: Stephen Hemminger
> Cc: Ouyang, Changchun; dev at dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v2 02/24] virtio: Use weaker barriers
>
>
>
> > -Original Message
> -Original Message-
> From: Stephen Hemminger [mailto:stephen at networkplumber.org]
> Sent: Tuesday, January 27, 2015 5:59 PM
> To: Xie, Huawei
> Cc: Ouyang, Changchun; dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2 02/24] virtio: Use weaker barriers
>
The DPDK driver only has to deal with the case of running on PCI
and with SMP. In this case, the code can use the weaker barriers
instead of using hard (fence) barriers. This will help performance.
The rationale is explained in Linux kernel virtio_ring.h.
To make it clearer that this is a virtio t
> I recall our original code is virtio_wmb().
> Use store fence to ensure all updates to entries before updating the index.
> Why do we need virtio_rmb() here and add virtio_wmb after
> vq_update_avail_idx()?
Store fence is unnecessary, Intel CPU's are cache coherent, please read
the virtio Lin
: Stephen Hemminger (stephen at networkplumber.org)
Subject: RE: [dpdk-dev] [PATCH v2 02/24] virtio: Use weaker barriers
>---if (likely(nb_enqueued)) {
>--->---virtio_wmb();
>--->---if (unlikely(virtqueue_kick_prepare(rxvq))) {
>--->--->
>---if (likely(nb_enqueued)) {
>--->---virtio_wmb();
>--->---if (unlikely(virtqueue_kick_prepare(rxvq))) {
>--->--->---virtqueue_notify(rxvq);
>--->--->---PMD_RX_LOG(DEBUG, "Notified\n");
>--->---}
>---}
>---vq_update_avail_idx(rxvq);
Tw
> -Original Message-
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ouyang Changchun
> Sent: Tuesday, January 27, 2015 10:36 AM
> To: dev at dpdk.org
> Subject: [dpdk-dev] [PATCH v2 02/24] virtio: Use weaker barriers
>
> The DPDK driver only has to
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