Re: [Xen-devel] [PATCH v2 3/3] xen: optimize xenbus driver for multiple concurrent xenstore accesses

[Juergen Gross <jgross@xxxxxxxx>]

On 18/01/17 21:14, Boris Ostrovsky wrote:
> On 01/16/2017 09:15 AM, Juergen Gross wrote:
>> +
>> +static uint32_t xs_request_enter(struct xb_req_data *req)
>> +{
>> +    uint32_t rq_id;
>> +
>> +    req->type = req->msg.type;
>> +
>> +    spin_lock(&xs_state_lock);
>> +    for (;;) {
>> +            if (req->msg.tx_id != 0)
>> +                    break;
>> +            if (xs_suspend_active) {
>> +                    spin_unlock(&xs_state_lock);
>> +                    wait_event(xs_state_enter_wq, xs_suspend_active == 0);
>> +                    spin_lock(&xs_state_lock);
>> +                    continue;
>> +            }
>> +            if (req->type == XS_TRANSACTION_START)
>> +                    xs_state_users++;
>> +            break;
>> +    }
>> +    xs_state_users++;
>> +    rq_id = xs_request_id++;
>> +    spin_unlock(&xs_state_lock);
>> +
>> +    return rq_id;
>> +}
> 
> I should have noticed this last time but I've been looking at this code
> again and I don't think I understand why you are incrementing count for
> XS_TRANSACTION_START inside the loop.
> 
> In fact, why not just 'while(xs_suspend_active) {}' loop?

That's a valid question.

I'll change it. The reason to have the larger loop body isn't existing
any longer.


Juergen


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