On 4/16/21 4:53 PM, Mike Snitzer wrote: > On Fri, Apr 16 2021 at 10:01am -0400, > Hannes Reinecke <hare@xxxxxxx> wrote: > >> On 4/16/21 1:15 AM, Mike Snitzer wrote: >>> From: Chao Leng <lengchao@xxxxxxxxxx> >>> >>> REQ_FAILFAST_TRANSPORT was designed for SCSI, because the SCSI protocol >>> does not define the local retry mechanism. SCSI implements a fuzzy >>> local retry mechanism, so REQ_FAILFAST_TRANSPORT is needed to allow >>> higher-level multipathing software to perform failover/retry. >>> >>> NVMe is different with SCSI about this. It defines a local retry >>> mechanism and path error codes, so NVMe should retry local for non >>> path error. If path related error, whether to retry and how to retry >>> is still determined by higher-level multipathing's failover. >>> >>> Unlike SCSI, NVMe shouldn't prevent retry if REQ_FAILFAST_TRANSPORT >>> because NVMe's local retry is needed -- as is NVMe specific logic to >>> categorize whether an error is path related. >>> >>> In this way, the mechanism of NVMe multipath or other multipath are >>> now equivalent. The mechanism is: non path related error will be >>> retried locally, path related error is handled by multipath. >>> >>> Signed-off-by: Chao Leng <lengchao@xxxxxxxxxx> >>> [snitzer: edited header for grammar and clarity, also added code comment] >>> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> >>> --- >>> drivers/nvme/host/core.c | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c >>> index 540d6fd8ffef..4134cf3c7e48 100644 >>> --- a/drivers/nvme/host/core.c >>> +++ b/drivers/nvme/host/core.c >>> @@ -306,7 +306,14 @@ static inline enum nvme_disposition nvme_decide_disposition(struct request *req) >>> if (likely(nvme_req(req)->status == 0)) >>> return COMPLETE; >>> >>> - if (blk_noretry_request(req) || >>> + /* >>> + * REQ_FAILFAST_TRANSPORT is set by upper layer software that >>> + * handles multipathing. Unlike SCSI, NVMe's error handling was >>> + * specifically designed to handle local retry for non-path errors. >>> + * As such, allow NVMe's local retry mechanism to be used for >>> + * requests marked with REQ_FAILFAST_TRANSPORT. >>> + */ >>> + if ((req->cmd_flags & (REQ_FAILFAST_DEV | REQ_FAILFAST_DRIVER)) || >>> (nvme_req(req)->status & NVME_SC_DNR) || >>> nvme_req(req)->retries >= nvme_max_retries) >>> return COMPLETE; >>> >> Huh? >> >> #define blk_noretry_request(rq) \ >> ((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \ >> REQ_FAILFAST_DRIVER)) >> >> making the only _actual_ change in your patch _not_ evaluating the >> REQ_FAILFAST_DRIVER, which incidentally is only used by the NVMe core. > > No, not sure how you got there. I'd have thought the 5 references to > "REQ_FAILFAST_TRANSPORT" would've been sufficient ;) > Ah. Misread stuff. You're excluding the REQ_FAILFAST_TRANSPORT here. But then it's _actually_ similar to the next patch (which I've also commented). Wouldn't it be better to fold them into one patch and discuss things together; especially as my comment to the next one might actually achieve the same thing? Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, 90409 Nürnberg GF: F. Imendörffer, HRB 36809 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
