Hi Jens, OK, I understand that. But I think that the block layer assumption (depending on "current") is not ideal. Anyway, thank you for the information. Thanks, Kiyoshi Ueda On Thu, 21 Dec 2006 08:53:05 +0100, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote: > On Wed, Dec 20 2006, Kiyoshi Ueda wrote: > > Hi Jens, > > > > On Wed, 20 Dec 2006 19:49:17 +0100, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote: > > > > > Big NACK on this - it's not only really ugly, it's also buggy to pass > > > > > interrupt flags as function arguments. As you also mention in the 0/1 > > > > > mail, this also breaks CFQ. > > > > > > > > > > Why do you need in-interrupt request allocation? > > > > > > > > Because I'd like to use blk_get_request() in q->request_fn() > > > > which can be called from interrupt context like below: > > > > scsi_io_completion -> scsi_end_request -> scsi_next_command > > > > -> scsi_run_queue -> blk_run_queue -> q->request_fn > > > > > > > > Generally, device-mapper (dm) clones an original I/O and dispatches > > > > the clones to underlying destination devices. > > > > In the request-based dm patch, the clone creation and the dispatch > > > > are done in q->request_fn(). To create the clone, blk_get_request() > > > > is used to get a request from underlying destination device's queue. > > > > By doing that in q->request_fn(), dm can deal with struct request > > > > after bios are merged by __make_request(). > > > > > > > > Do you think creating another function like blk_get_request_nowait() > > > > is acceptable? > > > > Or request should not be allocated in q->request_fn() anyway? > > > > > > You should not be allocating requests from that path, for a number of > > > reasons. > > > > Could I hear the reasons for my further work if possible? > > Because of breaking current CFQ? And is there any reason? > > Mainly I just don't like the design, there are better ways to achieve > what you need. The block layer has certain assumptions on the context > from which rq allocation happens, and this breaks it. As I also > mentioned, you cannot pass flags around as arguments. So the patch is > even broken as-is. > > -- > Jens Axboe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
