From: Mike Snitzer <firstname.lastname@example.org>
To: Hannes Reinecke <email@example.com>
Cc: Christoph Hellwig <firstname.lastname@example.org>, Jens Axboe <email@example.com>,
firstname.lastname@example.org, Chao Leng <email@example.com>
Subject: Re: [PATCH v2 2/4] nvme: allow local retry for requests with REQ_FAILFAST_TRANSPORT set
Date: Fri, 16 Apr 2021 11:32:59 -0400 [thread overview]
Message-ID: <20210416153259.GA20150@redhat.com> (raw)
On Fri, Apr 16 2021 at 11:20am -0400,
Hannes Reinecke <firstname.lastname@example.org> wrote:
> On 4/16/21 4:53 PM, Mike Snitzer wrote:
> > On Fri, Apr 16 2021 at 10:01am -0400,
> > Hannes Reinecke <email@example.com> wrote:
> >> On 4/16/21 1:15 AM, Mike Snitzer wrote:
> >>> From: Chao Leng <firstname.lastname@example.org>
> >>> 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 <email@example.com>
> >>> [snitzer: edited header for grammar and clarity, also added code comment]
> >>> Signed-off-by: Mike Snitzer <firstname.lastname@example.org>
> >>> ---
> >>> 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
> 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?
2 discrete things. This patch enables local retry.
Patch 3 allows proper failover via upper layer multipathing.
And as I replied, your suggestion about using DNR doesn't achieve the
same thing (said as much in reply to the patch 3 thread).
next prev parent reply other threads:[~2021-04-16 15:33 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-15 23:15 [PATCH v2 0/4] nvme: improve error handling and ana_state to work well with dm-multipath Mike Snitzer
2021-04-15 23:15 ` [PATCH v2 1/4] nvme: return BLK_STS_DO_NOT_RETRY if the DNR bit is set Mike Snitzer
2021-04-15 23:48 ` Chaitanya Kulkarni
2021-04-16 13:51 ` Hannes Reinecke
2021-04-15 23:15 ` [PATCH v2 2/4] nvme: allow local retry for requests with REQ_FAILFAST_TRANSPORT set Mike Snitzer
2021-04-16 14:01 ` Hannes Reinecke
2021-04-16 14:53 ` Mike Snitzer
2021-04-16 15:20 ` Hannes Reinecke
2021-04-16 15:32 ` Mike Snitzer [this message]
2021-04-15 23:15 ` [PATCH v2 3/4] nvme: introduce FAILUP handling for REQ_FAILFAST_TRANSPORT Mike Snitzer
2021-04-16 14:07 ` Hannes Reinecke
2021-04-16 15:03 ` Mike Snitzer
2021-04-16 16:23 ` Hannes Reinecke
2021-04-16 20:03 ` [dm-devel] " Ewan D. Milne
2021-04-16 20:52 ` Ewan D. Milne
2021-04-16 21:44 ` Mike Snitzer
2021-04-15 23:15 ` [PATCH v2 4/4] nvme: decouple basic ANA log page re-read support from native multipathing Mike Snitzer
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