Re: [uml-devel] patch: use elv_queue_empty

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Alle 22:11, domenica 8 febbraio 2004, Werner Almesberger ha scritto:
> This patch makes UBD a little more compatible with alternative
> elevators that may not use a single request queue.

> --- linux-2.6.1/arch/um/drivers/ubd_kern.c.orig	Sun Feb  8 17:16:51 2004
> +++ linux-2.6.1/arch/um/drivers/ubd_kern.c	Sun Feb  8 17:17:32 2004
> @@ -1034,7 +1034,7 @@
>  	int err, n;
>
>  	if(thread_fd == -1){
> -		while(!list_empty(&q->queue_head)){
> +		while(!elv_queue_empty(q)){
>  			req = elv_next_request(q);
>  			err = prepare_request(req, &io_req);
>  			if(!err){
> @@ -1044,7 +1044,7 @@
>  		}
>  	}
>  	else {
> -		if(do_ubd || list_empty(&q->queue_head)) return;
> +		if(do_ubd || elv_queue_empty(q)) return;
>  		req = elv_next_request(q);
>  		err = prepare_request(req, &io_req);
>  		if(!err){

The old code was basically wrong - but Documentation/block/biodoc.txt 
recommends using just elv_next_request - i.e. instead of looping until 
elv_queue_empty(q) is true, just loop until elv_next_request returns NULL.
Calling elv_queue_empty is meaningless to just check if queues are empty if we 
must not get a request right now, since that can save us the cost of 
dispatching pending requests. But this is not the case. So the code could 
become:

while (1) {
  req = elv_next_request(q);
  if (!req) break;
...}

and 

if(do_ubd) return;
req = elv_next_request(q);
if (!req) return;

Any idea against / in favour of this?
Bye
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729



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