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To: Tiwei Bie <tiwei.bie@intel.com>, Jens Freimann <jfreimann@redhat.com>
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From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Subject: Re: [dpdk-dev] [PATCH 05/10] net/virtio: refactor virtqueue
structure
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On 3/19/19 11:09 AM, Tiwei Bie wrote:
> On Tue, Mar 19, 2019 at 10:44:32AM +0100, Jens Freimann wrote:
>> On Tue, Mar 19, 2019 at 02:43:07PM +0800, Tiwei Bie wrote:
>>> Put split ring and packed ring specific fields into separate
>>> sub-structures, and also union them as they won't be available
>>> at the same time.
>>>
>>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
>>> ---
>>> drivers/net/virtio/virtio_ethdev.c | 71 +++++++++---------
>>> drivers/net/virtio/virtio_rxtx.c | 66 ++++++++---------
>>> drivers/net/virtio/virtio_rxtx_simple.h | 2 +-
>>> drivers/net/virtio/virtio_rxtx_simple_neon.c | 2 +-
>>> drivers/net/virtio/virtio_rxtx_simple_sse.c | 2 +-
>>> drivers/net/virtio/virtqueue.c | 6 +-
>>> drivers/net/virtio/virtqueue.h | 77 +++++++++++---------
>>> 7 files changed, 117 insertions(+), 109 deletions(-)
>>>
>> [snip]
>> ...
>>> diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
>>> index 80c0c43c3..48b3912e6 100644
>>> --- a/drivers/net/virtio/virtqueue.h
>>> +++ b/drivers/net/virtio/virtqueue.h
>>> @@ -191,17 +191,22 @@ struct vq_desc_extra {
>>>
>>> struct virtqueue {
>>> struct virtio_hw *hw; /**< virtio_hw structure pointer. */
>>> - struct vring vq_ring; /**< vring keeping desc, used and avail */
>>> - struct vring_packed ring_packed; /**< vring keeping descs */
>>> - bool used_wrap_counter;
>>> - uint16_t cached_flags; /**< cached flags for descs */
>>> - uint16_t event_flags_shadow;
>>> + union {
>>> + struct {
>>> + /**< vring keeping desc, used and avail */
>>> + struct vring ring;
>>> + } vq_split;
>>>
>>> - /**
>>> - * Last consumed descriptor in the used table,
>>> - * trails vq_ring.used->idx.
>>> - */
>>> - uint16_t vq_used_cons_idx;
>>> + struct {
>>> + /**< vring keeping descs and events */
>>> + struct vring_packed ring;
>>> + bool used_wrap_counter;
>>> + uint16_t cached_flags; /**< cached flags for descs */
>>> + uint16_t event_flags_shadow;
>>> + } vq_packed;
>>> + };
>>> +
>>> + uint16_t vq_used_cons_idx; /**< last consumed descriptor */
>>> uint16_t vq_nentries; /**< vring desc numbers */
>>> uint16_t vq_free_cnt; /**< num of desc available */
>>> uint16_t vq_avail_idx; /**< sync until needed */
>>
>> Honest question: What do we really gain by putting it in a union? We
>> save a little memory. But we also make code less readable IMHO.
>
> I think it will make it clear that fields like used_wrap_counter
> are only available in packed ring which will make the code more
> readable.
>
>>
>> If we do this, can we at least shorten some variable names, like drop
>> the vq_ prefix? (It's used everywhere like vq->vq_packed*, so with
>> vq->packed* we don't loose any context).
>
> I prefer to have consistent prefix like most fields in this
> structure (although some fields don't really follow this).
As Jens, I tend to agree that the vq_ prefix is quite redundant.
However, I think it is better to keep it in this patch for consistency.
Maybe it can be remove in a separate patch later?
> Thanks,
> Tiwei
>
>>
>> I'm not strictly against this change but I'm wondering if it's worth
>> it.
>>
>> regards,
>> Jens
>>
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To: Tiwei Bie <tiwei.bie@intel.com>, Jens Freimann <jfreimann@redhat.com>
Cc: zhihong.wang@intel.com, dev@dpdk.org
References: <20190319064312.13743-1-tiwei.bie@intel.com>
<20190319064312.13743-6-tiwei.bie@intel.com>
<20190319094432.iap4i7ffs6soukr7@jenstp.localdomain>
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From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Date: Tue, 19 Mar 2019 14:28:30 +0100
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(mx1.redhat.com [10.5.110.40]); Tue, 19 Mar 2019 13:28:33 +0000 (UTC)
Subject: Re: [dpdk-dev] [PATCH 05/10] net/virtio: refactor virtqueue
structure
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On 3/19/19 11:09 AM, Tiwei Bie wrote:
> On Tue, Mar 19, 2019 at 10:44:32AM +0100, Jens Freimann wrote:
>> On Tue, Mar 19, 2019 at 02:43:07PM +0800, Tiwei Bie wrote:
>>> Put split ring and packed ring specific fields into separate
>>> sub-structures, and also union them as they won't be available
>>> at the same time.
>>>
>>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
>>> ---
>>> drivers/net/virtio/virtio_ethdev.c | 71 +++++++++---------
>>> drivers/net/virtio/virtio_rxtx.c | 66 ++++++++---------
>>> drivers/net/virtio/virtio_rxtx_simple.h | 2 +-
>>> drivers/net/virtio/virtio_rxtx_simple_neon.c | 2 +-
>>> drivers/net/virtio/virtio_rxtx_simple_sse.c | 2 +-
>>> drivers/net/virtio/virtqueue.c | 6 +-
>>> drivers/net/virtio/virtqueue.h | 77 +++++++++++---------
>>> 7 files changed, 117 insertions(+), 109 deletions(-)
>>>
>> [snip]
>> ...
>>> diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
>>> index 80c0c43c3..48b3912e6 100644
>>> --- a/drivers/net/virtio/virtqueue.h
>>> +++ b/drivers/net/virtio/virtqueue.h
>>> @@ -191,17 +191,22 @@ struct vq_desc_extra {
>>>
>>> struct virtqueue {
>>> struct virtio_hw *hw; /**< virtio_hw structure pointer. */
>>> - struct vring vq_ring; /**< vring keeping desc, used and avail */
>>> - struct vring_packed ring_packed; /**< vring keeping descs */
>>> - bool used_wrap_counter;
>>> - uint16_t cached_flags; /**< cached flags for descs */
>>> - uint16_t event_flags_shadow;
>>> + union {
>>> + struct {
>>> + /**< vring keeping desc, used and avail */
>>> + struct vring ring;
>>> + } vq_split;
>>>
>>> - /**
>>> - * Last consumed descriptor in the used table,
>>> - * trails vq_ring.used->idx.
>>> - */
>>> - uint16_t vq_used_cons_idx;
>>> + struct {
>>> + /**< vring keeping descs and events */
>>> + struct vring_packed ring;
>>> + bool used_wrap_counter;
>>> + uint16_t cached_flags; /**< cached flags for descs */
>>> + uint16_t event_flags_shadow;
>>> + } vq_packed;
>>> + };
>>> +
>>> + uint16_t vq_used_cons_idx; /**< last consumed descriptor */
>>> uint16_t vq_nentries; /**< vring desc numbers */
>>> uint16_t vq_free_cnt; /**< num of desc available */
>>> uint16_t vq_avail_idx; /**< sync until needed */
>>
>> Honest question: What do we really gain by putting it in a union? We
>> save a little memory. But we also make code less readable IMHO.
>
> I think it will make it clear that fields like used_wrap_counter
> are only available in packed ring which will make the code more
> readable.
>
>>
>> If we do this, can we at least shorten some variable names, like drop
>> the vq_ prefix? (It's used everywhere like vq->vq_packed*, so with
>> vq->packed* we don't loose any context).
>
> I prefer to have consistent prefix like most fields in this
> structure (although some fields don't really follow this).
As Jens, I tend to agree that the vq_ prefix is quite redundant.
However, I think it is better to keep it in this patch for consistency.
Maybe it can be remove in a separate patch later?
> Thanks,
> Tiwei
>
>>
>> I'm not strictly against this change but I'm wondering if it's worth
>> it.
>>
>> regards,
>> Jens
>>