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? > The design isn't very nice either. > > The easy way out would be to punt to a workqueue to handle the requests. > > An alternative way would be to set aside some requests that you can get > at without allocation (maintain a little freelist of manually allocated > requests), and retrieve a free one from there when inside request_fn. If > you run out, just bail out of request_fn and make sure to reinvoke it > when some of your previously issued requests complete and are added back > to that freelist. Thank you for the suggestions. OK, I'll think other designs based on your suggestions. Thanks, Kiyoshi Ueda -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
