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 ;) This patch makes it so requests marked with REQ_FAILFAST_TRANSPORT are allowed to use NVMe's local retry (that is required for non-transport errors). > So what is it you're trying to solve? What the patch header, code and code comment detail. Mike
