Re: [PATCH 3/3] nvme: add parameter command_retry to enable retry

[Minwoo Im <minwoo.im.dev@gmail.com>]

Hello,

On 21-01-12 17:34:48, Chao Leng wrote:
> 
> 
> On 2021/1/11 20:27, Minwoo Im wrote:
> > Hello,
> > 
> > On 21-01-11 11:47:56, Chao Leng wrote:
> > > 
> > > 
> > > On 2021/1/8 22:46, Minwoo Im wrote:
> > > > nvme_init_request() has set REQ_FAILFAST_DRIVER to make requests
> > > > non-retryable.  This command flag value is checked in
> > > > nvme_decide_disposition() to decide whether to RETRY or other
> > > > operations.  In that point, blk_noretry_request() macro will be used to
> > > > check if command flags have one of REQ_FAILFAST_*.  If so, it just
> > > > decides to complete the request without retrying.
> > > > 
> > > > This patch added a module parameter named command_retry to turn on the
> > > > command retry feature in this driver.  If turning it on,
> > > > REQ3_FAILFAST_DRIVER will not be set to requests so that retry can be
> > > > reached out to nvme_retry_req() based on the module parameter.
> > > > 
> > > > Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
> > > > ---
> > > >    drivers/nvme/host/core.c | 7 ++++++-
> > > >    1 file changed, 6 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> > > > index 6e428fdc25a8..e1836ca9956f 100644
> > > > --- a/drivers/nvme/host/core.c
> > > > +++ b/drivers/nvme/host/core.c
> > > > @@ -44,6 +44,10 @@ static unsigned char shutdown_timeout = 5;
> > > >    module_param(shutdown_timeout, byte, 0644);
> > > >    MODULE_PARM_DESC(shutdown_timeout, "timeout in seconds for controller shutdown");
> > > > +static bool command_retry;
> > > > +module_param(command_retry, bool, 0644);
> > > > +MODULE_PARM_DESC(command_retry, "retry commands up to nvme_max_retries");
> > > > +
> > > >    static u8 nvme_max_retries = 5;
> > > >    module_param_named(max_retries, nvme_max_retries, byte, 0644);
> > > >    MODULE_PARM_DESC(max_retries, "max number of retries a command may have");
> > > > @@ -560,7 +564,8 @@ static inline void nvme_init_request(struct request *req,
> > > >    	else /* no queuedata implies admin queue */
> > > >    		req->timeout = NVME_ADMIN_TIMEOUT;
> > > > -	req->cmd_flags |= REQ_FAILFAST_DRIVER;
> > > > +	if (!command_retry)
> > > > +		req->cmd_flags |= REQ_FAILFAST_DRIVER;
> > > In abnormal scenarios, such as request time out, connection process may takes long time or the admin command waits for long time.
> > > Retry only for non-host errors may be a better choice. Maybe we can make some optimizations in nvme_decide_disposition.
> > 
> > Thanks for your review!
> > 
> > Oh, I agreed that it might wait for so long time in connecting process.
> > Restricting some of commands that should be retried would be better as
> > you mentiond.
> > 
> > Do you mean that maybe we can check this module parameter in
> > nvme_decide_disposition()?  Like, even if blk_noretry_request(req) says
> > that it's non-retriable, if this module parameter is enabled, then we
> > can retry rather than failfast?
> No, I mean that add the local preferential retry which defined in the NVMe protocol.

Thanks for your suggestion, Chao.  I think this is much better idea than
module parameter.  Fixing the nvme_decide_disposition() would be better!
I think it's going to be also an answer for Christoph's question on this
patch.  Please let me prepare next pach series.

Thanks,

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