From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH 06/12] scsi_transport_srp: Reduce failover time Date: Thu, 30 Apr 2015 13:02:02 +0200 Message-ID: <55420BAA.7060507@sandisk.com> References: <5541EE21.3050809@sandisk.com> <5541EF01.3030008@sandisk.com> <5542002D.8060308@dev.mellanox.co.il> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5542002D.8060308@dev.mellanox.co.il> Sender: linux-scsi-owner@vger.kernel.org To: Sagi Grimberg , Doug Ledford Cc: James Bottomley , Sagi Grimberg , Sebastian Parschauer , linux-rdma , "linux-scsi@vger.kernel.org" List-Id: linux-rdma@vger.kernel.org On 04/30/15 12:13, Sagi Grimberg wrote: > 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? The purpose of the srp_timed_out() function is not about failing commands early but about postponing timeout errors. The above patch causes a SCSI timeout to be handled as soon as the command timer expires if rport->fast_io_fail_tmo >= 0 or rport->dev_loss_tmo >= 0. Bart.