Hello, We would like to know in which kernel version these patches are available. Thanks, Chandrakala -----Original Message----- From: linux-scsi-owner@xxxxxxxxxxxxxxx [mailto:linux-scsi-owner@xxxxxxxxxxxxxxx] On Behalf Of Jens Axboe Sent: Monday, September 03, 2007 1:16 PM To: Kiyoshi Ueda Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-scsi@xxxxxxxxxxxxxxx; linux-ide@xxxxxxxxxxxxxxx; Miller, Mike (OS Dev); grant.likely@xxxxxxxxxxxx; dm-devel@xxxxxxxxxx; j-nomura@xxxxxxxxxxxxx Subject: Re: [PATCH 0/7] blk_end_request: full I/O completion handler On Fri, Aug 31 2007, Kiyoshi Ueda wrote: > Hello, > > This set of patches changes request completion interface between > device drivers and block layer to 1 step procedure from current 2 step > procedures using end_that_request_{first/chunk} and > end_that_request_last(). > > This change allows request-based multipath to hook in before > completing each chunk of request, check errors for it and retry it > using another path if error is detected. > > Summaries of each patch are below: > 1/7: add new request completion interface, blk_end_request() > 2/7: add some macros to get the size of request in bytes > 3/7: convert normal drivers to use blk_end_request() > 4/7: convert odd drivers like cciss/cpqarray/xsysace to use > blk_end_request() > 5/7: convert ide-cd (cdrom_newpc_intr) to use blk_end_request() > 6/7: remove/unexport no longer needed end_that_request_* > 7/7: change rq->end_io to cover request completion as a whole > > I have tested the patch on two machines, ia64+QLA1280+QLA2200 and > x86_64+SATA+IDE-CDROM. > I can't test other device drivers for which I don't have hardware. > So testing help and any comments would be very much appreciated. > > The interface change causes code modifications of *ALL DEVICE DRIVERS* > which are using end_that_request_{first/chunk/last} to complete request. > But it should not affect the behavior. > > Please review and apply if no problem. > This patch-set should be applied on top of 2.6.23-rc3-mm1. > > > BACKGROUND > ========== > The patch is necessary to allow device stacking at request level, that > is request-based device-mapper multipath. > Currently, device-mapper is implemented as a stacking block device at > BIO level. OTOH, request-based DM will stack at request level to > allow better multipathing decision. > To allow device stacking at request level, the completion procedure > need to provide a hook for it. > For example, dm-multipath has to check errors and retry with other > paths if necessary before returning the I/O result to upper layer. > struct request has 'end_io' hook currently. But it's called at the > very late stage of completion handling where the I/O result is already > returned to the upper layer. > So we need something here. > > The first approach to hook in completion of each chunk of request was > adding a new rq->end_io_first() hook and calling it on the top of > __end_that_request_first(). > - http://marc.theaimsgroup.com/?l=linux-scsi&m=115520444515914&w=2 > - http://marc.theaimsgroup.com/?l=linux-kernel&m=116656637425880&w=2 > However, Jens pointed out that redesigning rq->end_io() as a full > completion handler would be better: > > On Thu, 21 Dec 2006 08:49:47 +0100, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote: > > Ok, I see what you are getting at. The current ->end_io() is called > > when the request has fully completed, you want notification for each > > chunk potentially completed. > > > > I think a better design here would be to use ->end_io() as the full > > completion handler, similar to how bio->bi_end_io() works. A request > > originating from __make_request() would set something ala: > ..... > > instead of calling the functions manually. That would allow you to > > get notification right at the beginning and do what you need, > > without adding a special hook for this. > > I thought his comment was reasonable. > So I modified the patches based on his suggestion. > > > WHAT IS CHANGED > =============== > The change is basically illustlated by the following pseudo code: > > [Before] > if (end_that_request_{first/chunk} succeeds) { <-- completes bios > <do something driver specific> > end_that_request_last() <-- calls end_io() > <the request is free from the driver> > } else { > <the request was incomplete, retry for leftover or ignoring> > } > > [After] > if (blk_end_request() succeeds) { <-- calls end_io(), completes bios > <the request is free from the driver> > } else { > <the request was incomplete, retry for leftover or ignoring> > } > > > In detail, request completion procedures are changed like below. > > [Before] > o 2 steps completion using end_that_request_{first/chunk} > and end_that_request_last(). > o Device drivers have ownership of a request until they > call end_that_request_last(). > o rq->end_io() is called at the last stage of > end_that_request_last() for some block layer codes need > specific request handling when completing it. > > [After] > o 1 step completion using blk_end_request(). > (end_that_request_* are no longer used from device drivers.) > o Device drivers give over ownership of a request > when calling blk_end_request(). > If it returns 0, the request is completed. > If it returns 1, the request isn't completed and > the ownership is returned to the device driver again. > o rq->end_io() is called at the top of blk_end_request() to > allow to hook all parts of request completion. > Existing users of rq->end_io() must be changed to do > all parts of request completion. > > > EXAMPLE CODE > ============ > Request-based Device-mapper multipath patch-set is attached as > appendix, although it still needs some work and isn't ready for review. > It checks error of a request and retries the request using other paths > if error is detected, before completing bios in the request. > (See clone_end_request() in appendix#1.) This looks good, thanks for following up on this! I've replied with comments on changes for the core bits, the interface I quite agree with. So if you fix up the things I ask for, I'll merge this up. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
