linux-kernel - Re: [PATCH v2 3/4] virtio_test: use random length scatterlists to test descriptor chain

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Date:   Thu, 7 Jul 2022 14:24:02 +0800
From:   Guo Zhi <qtxuning1999@...u.edu.cn>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     jasowang@...hat.com, eperezma@...hat.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, sgarzare@...hat.com
Subject: Re: [PATCH v2 3/4] virtio_test: use random length scatterlists to
 test descriptor chain

On 2022/7/7 13:16, Michael S. Tsirkin wrote:
> On Thu, Jul 07, 2022 at 10:44:08AM +0800, Guo Zhi wrote:
>> Prior implementation only use one descriptor for each io event, which
>> does't test code of descriptor chain. More importantly, one descriptor
>> will not use indirect feature even indirect feature is specified. Use
>> random length scatterlists here to test descriptor chain.
>>
>> Signed-off-by: Guo Zhi <qtxuning1999@...u.edu.cn>
>> ---
>>   tools/virtio/virtio_test.c | 11 ++++++++---
>>   1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/virtio/virtio_test.c b/tools/virtio/virtio_test.c
>> index 1ecd64271..363695b33 100644
>> --- a/tools/virtio/virtio_test.c
>> +++ b/tools/virtio/virtio_test.c
>> @@ -20,6 +20,7 @@
>>   #include "../../drivers/vhost/test.h"
>>   
>>   #define RANDOM_BATCH -1
>> +#define MAX_SG_FRAGS 8UL
>>   #define ALIGN 4096
>>   #define RINGSIZE   256
>>   #define TEST_BUF_NUM 0x100000
>> @@ -172,7 +173,8 @@ static void wait_for_interrupt(struct vdev_info *dev)
>>   static void run_test(struct vdev_info *dev, struct vq_info *vq,
>>   		     bool delayed, int batch, int reset_n, int bufs)
>>   {
>> -	struct scatterlist sl;
>> +	struct scatterlist sg[MAX_SG_FRAGS];
>> +	int sg_size = 0;
>>   	long started = 0, completed = 0, next_reset = reset_n;
>>   	long completed_before, started_before;
>>   	int r, test = 1;
>> @@ -197,8 +199,11 @@ static void run_test(struct vdev_info *dev, struct vq_info *vq,
>>   
>>   			while (started < bufs &&
>>   			       (started - completed) < batch) {
>> -				sg_init_one(&sl, dev->buf, dev->buf_size);
>> -				r = virtqueue_add_outbuf(vq->vq, &sl, 1,
>> +				sg_size = random() % (MAX_SG_FRAGS - 1) + 1;
>> +				sg_init_table(sg, sg_size);
>> +				for (int i = 0; i < sg_size; ++i)
>> +					sg_set_buf(&sg[i], dev->buf + i, 0x1);
>> +				r = virtqueue_add_outbuf(vq->vq, sg, sg_size,
>>   							 dev->buf + started,
>>   							 GFP_ATOMIC);
>>   				if (unlikely(r != 0)) {
> random on data path is pretty expensive.
> I would suggest get an array size from user (and maybe a seed?) and
> pregenerate some numbers, then reuse.
SGTM, I will prepare a random number array before add outbuf begin.
>
>> -- 
>> 2.17.1