On Thu, Oct 20, 2005 at 02:25:05PM +0200, Jens Axboe wrote:
> On Wed, Oct 19 2005, Tejun Heo wrote:
> > Hello, Jens.
> >
> > This patch reimplements elevator switch. This patch assumes generic
> > dispatch queue patchset is applied.
> >
> > * Each request is tagged with REQ_ELVPRIV flag if it has its elevator
> > private data set.
> > * Requests which doesn't have REQ_ELVPRIV flag set never enter
> > iosched. They are always directly back inserted to dispatch queue.
> > Of course, elevator_put_req_fn is called only for requests which
> > have its REQ_ELVPRIV set.
> > * Request queue maintains the current number of requests which have
> > its elevator data set (elevator_set_req_fn called) in
> > q->rq->elvpriv.
> > * If a request queue has QUEUE_FLAG_BYPASS set, elevator private data
> > is not allocated for new requests.
> >
> > To switch to another iosched, we set QUEUE_FLAG_BYPASS and wait until
> > elvpriv goes to zero; then, we attach the new iosched and clears
> > QUEUE_FLAG_BYPASS. New implementation is much simpler and main code
> > paths are less cluttered, IMHO.
>
> Wonderful! Applied as-is, I didn't make any changes to this one. I agree
> it's much cleaner than the previous approach, both in the code and in
> killing the request_queue and request_list members.
>
> I'm going to make a little few tweaks:
>
> - The naming, QUEUE_FLAG_BYPASS isn't really clear. I don't know what
> this means without looking at specific parts of the code. Testing of
It means to bypass ioscheds and go directly into dispatch queue.
> same flag in various locations would also be preferred instead of
> passing priv around and cluttering the function parameters, however we
> should split the queue flags a little for this. Basically into an
> atomic and non-atomic part. So I'll leave that alone for now.
Hmmm...
> - The msleep(100) seems a little too slow. With the switching being more
> efficient now, in 100msecs we can complete lots of requests.
Yeap, agreed.
--
tejun
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