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SubjectRe: [PATCH] Fix disk statistic reporting to include all disks
On Wed, Aug 30 2000, Bill Wilson wrote:
> Won't we loose some important info by not looking at minors? hda and
> hdb are minors of IDE0_MAJOR, etc. Is this data distinguishable in the
> queues?

hda and hdb each have their own queue, so we don't loose anything
there.

> > No big deal, for now I just have the proc code doing blk_get_queue for
> > every major. That code is hardly performance critical ;-)
>
> True for the kernel, but there are some user land apps that read /proc/stat
> quite frequently (10 per second) so some performance tuning might be
> worth it. There could be a linked list field in the blk_dev[] array
> which links all entries that have had statistics collected. Then the /proc
> code does not have to blk_get_queue on every major.

Right now the code in my tree looks something like this:

for (i = 0; i < MAX_BLKDEV; i++) {
request_queue_t *q = blk_get_queue(MKDEV(i, 0));
if (!q)
continue;
if (!active)
continue;

/* print stats */
}

So it's not really that bad. I suppose things could be made quicker
by just browsing a list of active queues, but I'm not sure it's worth
the trouble (but hey, proove me wrong). Note that linking blk_dev
does not make much sense, since not all queues are available from
there. Drivers are free to use their own queue, even several if they
want.

--
* Jens Axboe <axboe@suse.de>
* SuSE Labs
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