Hi,
As per my understanding the block layer clusters requests for all
block drivers.
Clustering -
Creating a linked list of buffer_heads using b_reqnext.
But, when I run my block driver and try to view the number of
clustered requests in my Request function, I do not find any
clustering done.
void own_request(request_queue_t *q)
{
struct buffer_head *tmp;
int count;
while(1) {
INIT_REQUEST;
printk("<1>request %p: cmd %i sec %li (nr. %li)\n", CURRENT,
CURRENT->cmd,
CURRENT->sector,
CURRENT->current_nr_sectors);
count=0;
for (tmp=bh; tmp; tmp=tmp->b_reqnext)
count ++;
printk("Count = %d\n", count);
end_request(1); /* success */
}
}
The above always shows 'Count = 1'. dd if=/dev/mydevice of=/dev/null.
Does this mean that no clustering is done ??
Just read a document a "http://www.usenix.org/publications/library/proceedings/usenix2000/freenix/full_papers/gopinath/gopinath_html/node14.html"
which says "This clustering is performed only for the drivers compiled in the kernel and not for loadable modules."
Is this the reason ??
Regards,
Mala
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