From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sagi Grimberg Subject: Re: [PATCH 06/12] scsi_transport_srp: Reduce failover time Date: Thu, 30 Apr 2015 13:13:01 +0300 Message-ID: <5542002D.8060308@dev.mellanox.co.il> References: <5541EE21.3050809@sandisk.com> <5541EF01.3030008@sandisk.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5541EF01.3030008@sandisk.com> Sender: linux-scsi-owner@vger.kernel.org To: Bart Van Assche , Doug Ledford Cc: James Bottomley , Sagi Grimberg , Sebastian Parschauer , linux-rdma , "linux-scsi@vger.kernel.org" List-Id: linux-rdma@vger.kernel.org On 4/30/2015 11:59 AM, Bart Van Assche wrote: > Unlike FC, there is no risk that SCSI devices will be offlined > by the error handler if it is started while a reconnect attempt > is ongoing. Hence report timeout errors as soon as possible > if a higher software layer (e.g. multipathd) needs to be informed > about a timeout. It is assumed that if both fast_io_fail_tmo < 0 > and rport->dev_loss_tmo < 0 that this means that there is no > need to report timeouts quickly. > > Signed-off-by: Bart Van Assche > Cc: James Bottomley > Cc: Sagi Grimberg > Cc: Sebastian Parschauer > --- > drivers/scsi/scsi_transport_srp.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/scsi/scsi_transport_srp.c b/drivers/scsi/scsi_transport_srp.c > index 4a44337..6667c2b 100644 > --- a/drivers/scsi/scsi_transport_srp.c > +++ b/drivers/scsi/scsi_transport_srp.c > @@ -61,6 +61,11 @@ static inline struct Scsi_Host *rport_to_shost(struct srp_rport *r) > return dev_to_shost(r->dev.parent); > } > > +static inline struct srp_rport *shost_to_rport(struct Scsi_Host *shost) > +{ > + return transport_class_to_srp_rport(&shost->shost_gendev); > +} > + > /** > * srp_tmo_valid() - check timeout combination validity > * @reconnect_delay: Reconnect delay in seconds. > @@ -626,9 +631,11 @@ static enum blk_eh_timer_return srp_timed_out(struct scsi_cmnd *scmd) > struct scsi_device *sdev = scmd->device; > struct Scsi_Host *shost = sdev->host; > struct srp_internal *i = to_srp_internal(shost->transportt); > + struct srp_rport *rport = shost_to_rport(shost); > > pr_debug("timeout for sdev %s\n", dev_name(&sdev->sdev_gendev)); > - return i->f->reset_timer_if_blocked && scsi_device_blocked(sdev) ? > + return rport->fast_io_fail_tmo < 0 && rport->dev_loss_tmo < 0 && > + i->f->reset_timer_if_blocked && scsi_device_blocked(sdev) ? > BLK_EH_RESET_TIMER : BLK_EH_NOT_HANDLED; > } > > I'm not sure I understand the purpose of this patch? If the user requested fast_io_fail_tmo of X, I would assume it wants srp to retry for the command for X secs. Why should we fail it any earlier than that? There is a situation where I've seen srp starting the fast_io_fail_tmo later than expected because the QP retry exceeded error completion arrives late for certain workloads. Was this the motivation for this patch? Sagi.