Subject: Re: [PATCH net-next V2 3/3] virtio-net: rx busy polling support

From: Varka Bhadram <[email-masked]>
Date: Thu, 17 Jul 2014 08:57:54 +0530

On Thursday 17 July 2014 08:25 AM, Jason Wang wrote:
> On 07/16/2014 04:38 PM, Varka Bhadram wrote:
>> On 07/16/2014 11:51 AM, Jason Wang wrote:
>>> Add basic support for rx busy polling.
>>>
>>> Test was done between a kvm guest and an external host. Two hosts were
>>> connected through 40gb mlx4 cards. With both busy_poll and busy_read
>>> are set to 50 in guest, 1 byte netperf tcp_rr shows 116% improvement:
>>> transaction rate was increased from 9151.94 to 19787.37.
>>>
>>> Cc: Rusty Russell <[email-masked]>
>>> Cc: Michael S. Tsirkin <[email-masked]>
>>> Cc: Vlad Yasevich <[email-masked]>
>>> Cc: Eric Dumazet <[email-masked]>
>>> Signed-off-by: Jason Wang <[email-masked]>
>>> ---
>>>    drivers/net/virtio_net.c | 190
>>> ++++++++++++++++++++++++++++++++++++++++++++++-
>>>    1 file changed, 187 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index e417d93..4830713 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -27,6 +27,7 @@
>>>    #include <linux/slab.h>
>>>    #include <linux/cpu.h>
>>>    #include <linux/average.h>
>>> +#include <net/busy_poll.h>
>>>      static int napi_weight = NAPI_POLL_WEIGHT;
>>>    module_param(napi_weight, int, 0444);
>>> @@ -94,8 +95,143 @@ struct receive_queue {
>>>          /* Name of this receive queue: input.$index */
>>>        char name[40];
>>> +
>>> +#ifdef CONFIG_NET_RX_BUSY_POLL
>>> +    unsigned int state;
>>> +#define VIRTNET_RQ_STATE_IDLE        0
>>> +#define VIRTNET_RQ_STATE_NAPI         1    /* NAPI or refill owns
>>> this RQ */
>>> +#define VIRTNET_RQ_STATE_POLL         2    /* poll owns this RQ */
>>> +#define VIRTNET_RQ_STATE_DISABLED    4    /* RQ is disabled */
>>> +#define VIRTNET_RQ_OWNED (VIRTNET_RQ_STATE_NAPI |
>>> VIRTNET_RQ_STATE_POLL)
>>> +#define VIRTNET_RQ_LOCKED (VIRTNET_RQ_OWNED |
>>> VIRTNET_RQ_STATE_DISABLED)
>>> +#define VIRTNET_RQ_STATE_NAPI_YIELD  8    /* NAPI or refill yielded
>>> this RQ */
>>> +#define VIRTNET_RQ_STATE_POLL_YIELD  16   /* poll yielded this RQ */
>>> +    spinlock_t lock;
>>> +#endif  /* CONFIG_NET_RX_BUSY_POLL */
>>>    };
>>>    +#ifdef CONFIG_NET_RX_BUSY_POLL
>>> +static inline void virtnet_rq_init_lock(struct receive_queue *rq)
>>> +{
>>> +
>>> +    spin_lock_init(&rq->lock);
>>> +    rq->state = VIRTNET_RQ_STATE_IDLE;
>>> +}
>>> +
>>> +/* called from the device poll routine or refill routine to get
>>> ownership of a
>>> + * receive queue.
>>> + */
>>> +static inline bool virtnet_rq_lock_napi_refill(struct receive_queue
>>> *rq)
>>> +{
>>> +    int rc = true;
>>> +
>> bool instead of int...?
> Yes, it was better.
>>> +    spin_lock(&rq->lock);
>>> +    if (rq->state & VIRTNET_RQ_LOCKED) {
>>> +        WARN_ON(rq->state & VIRTNET_RQ_STATE_NAPI);
>>> +        rq->state |= VIRTNET_RQ_STATE_NAPI_YIELD;
>>> +        rc = false;
>>> +    } else
>>> +        /* we don't care if someone yielded */
>>> +        rq->state = VIRTNET_RQ_STATE_NAPI;
>>> +    spin_unlock(&rq->lock);
>> Lock for rq->state ...?
>>
>> If yes:
>> spin_lock(&rq->lock);
>> if (rq->state & VIRTNET_RQ_LOCKED) {
>>      rq->state |= VIRTNET_RQ_STATE_NAPI_YIELD;
>>      spin_unlock(&rq->lock);
>>      WARN_ON(rq->state & VIRTNET_RQ_STATE_NAPI);
>>      rc = false;
>> } else {
>>      /* we don't care if someone yielded */
>>      rq->state = VIRTNET_RQ_STATE_NAPI;
>>      spin_unlock(&rq->lock);
>> }
> I didn't see any differences. Is this used to catch the bug of driver
> earlier? btw, several other rx busy polling capable driver does the same
> thing.

We need not to include WARN_ON() & rc=false under critical section.

-- 
Regards,
Varka Bhadram