Linux-Block Archive on lore.kernel.org
 help / color / Atom feed
From: Mike Snitzer <snitzer@redhat.com>
To: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	dm-devel@redhat.com, linux-block@vger.kernel.org,
	linux-nvme@lists.infradead.org, Chao Leng <lengchao@huawei.com>
Subject: Re: [PATCH v2 2/4] nvme: allow local retry for requests with REQ_FAILFAST_TRANSPORT set
Date: Fri, 16 Apr 2021 10:53:40 -0400
Message-ID: <20210416145340.GB16047@redhat.com> (raw)
In-Reply-To: <da184561-2c97-5807-5c5b-9cc6593693c6@suse.de>

On Fri, Apr 16 2021 at 10:01am -0400,
Hannes Reinecke <hare@suse.de> wrote:

> On 4/16/21 1:15 AM, Mike Snitzer wrote:
> > From: Chao Leng <lengchao@huawei.com>
> > 
> > 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@huawei.com>
> > [snitzer: edited header for grammar and clarity, also added code comment]
> > Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> > ---
> >  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


  reply index

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 [this message]
2021-04-16 15:20       ` Hannes Reinecke
2021-04-16 15:32         ` Mike Snitzer
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210416145340.GB16047@redhat.com \
    --to=snitzer@redhat.com \
    --cc=axboe@kernel.dk \
    --cc=dm-devel@redhat.com \
    --cc=hare@suse.de \
    --cc=hch@lst.de \
    --cc=lengchao@huawei.com \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-nvme@lists.infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Block Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-block/0 linux-block/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-block linux-block/ https://lore.kernel.org/linux-block \
		linux-block@vger.kernel.org
	public-inbox-index linux-block

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-block


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git