On 7/5/19 9:44 AM, Stefan Hajnoczi wrote: > On Fri, Jul 05, 2019 at 09:12:37AM +0200, Hannes Reinecke wrote: >> On 7/4/19 3:19 PM, Paolo Bonzini wrote: >>> On 19/06/19 12:31, Paolo Bonzini wrote: >>>>> I'm a bit unsure if 'bd->last' is always set; it's quite obvious that >>>>> it's present if set, but what about requests with 'bd->last == false' ? >>>>> Is there a guarantee that they will _always_ be followed with a request >>>>> with bd->last == true? >>>>> And if so, is there a guarantee that this request is part of the same batch? >>>> It's complicated. A request with bd->last == false _will_ always be >>>> followed by a request with bd->last == true in the same batch. However, >>>> due to e.g. errors it may be possible that the last request is not sent. >>>> In that case, the block layer sends commit_rqs, as documented in the >>>> comment above, to flush the requests that have been sent already. >>>> >>>> So, a driver that obeys bd->last (or SCMD_LAST) but does not implement >>>> commit_rqs is bound to have bugs, which is why this patch was not split >>>> further. >>>> >>>> Makes sense? >>> >>> Hannes, can you provide your Reviewed-by? >>> >> Well ... since you asked for it: >> >> Where is the 'commit_rqs' callback actually used? >> I seem to be going blind, but I can't find it; should be somewhere in >> the first patch, no? >> As per description: >> >> * The commit_rqs function is used to trigger a hardware >> * doorbell after some requests have been queued with >> * queuecommand, when an error is encountered before sending >> * the request with SCMD_LAST set. >> >> So it should be somewhere in the error path, probably scsi_error or >> something. But I don't seem to be able to find it ... > > The block layer calls scsi_mq_ops->commit_rqs() from > blk_mq_dispatch_rq_list() and blk_mq_try_issue_list_directly(). > Ah, right. Now, then: Reviewed-by: Hannes Reinecke <hare@xxxxxxxx> Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Felix Imendörffer, Mary Higgins, Sri Rasiah HRB 21284 (AG Nürnberg)
