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SubjectRe: [PATCH net-next 1/3] vhost: generalize adding used elem
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On 2018/12/14 上午3:41, Michael S. Tsirkin wrote:
> On Thu, Dec 13, 2018 at 06:10:20PM +0800, Jason Wang wrote:
>> Use one generic vhost_copy_to_user() instead of two dedicated
>> accessor. This will simplify the conversion to fine grain accessors.
>>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>
> The reason we did it like this is because it was faster.
> Want to try benchmarking before we change it?


Faster is a good side effect of such conversion. Otherwise we need two
new fine grain memory accessor.

But, anyway, I can test its impact.

Thanks


>
>> ---
>> drivers/vhost/vhost.c | 11 +----------
>> 1 file changed, 1 insertion(+), 10 deletions(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 3a5f81a66d34..1c54ec1b82f8 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -2164,16 +2164,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
>>
>> start = vq->last_used_idx & (vq->num - 1);
>> used = vq->used->ring + start;
>> - if (count == 1) {
>> - if (vhost_put_user(vq, heads[0].id, &used->id)) {
>> - vq_err(vq, "Failed to write used id");
>> - return -EFAULT;
>> - }
>> - if (vhost_put_user(vq, heads[0].len, &used->len)) {
>> - vq_err(vq, "Failed to write used len");
>> - return -EFAULT;
>> - }
>> - } else if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
>> + if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
>> vq_err(vq, "Failed to write used");
>> return -EFAULT;
>> }
>> --
>> 2.17.1

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