Re: [PATCH 0/5] scsi: Allow fast io fail without waiting throughtimeout

[James Smart]

yes - that was the session. Granted the posted notes were rather terse.

More of the ideas were presented in this recent email thread: 
http://marc.info/?l=linux-scsi&m=136819142000596&w=2

In general - we're going to create a LLD library for error handling, 
using paradigms in libsas, that:
- no longer stops the whole host on the 1st error and doesn't start 
error handling till all outstanding io is finished/timedout
- sends per-io aborts immediately, and in parallel. LLD handlers will be 
asynchronous.
- no lun/target will be stopped until i/o aborts start to fail.
- do smart handling of lun resets, target resets, bus resets, etc and 
don't potentially do it for every i/o.

Several of these topics were touched on in the email thread.

the patches are being worked on now - hopefully to be posted as an RFC 
within the next couple of weeks.

-- james s



On 5/22/2013 3:12 AM, Ren Mingxin wrote:
> Hi, James,
>
> On 05/20/2013 11:53 PM, James Smart wrote:
> > Based on the discussion recently held at LSF 2013, we are
> > reworking the error recovery path to address all the issues
> > you are mentioning. That work contradicts these patches.
> > So for now, these should be held off.
>
> Interesting. Can I have your general goal/idea briefly even
> though via a reference? Will the URL below be one you will
> refer to?
>   http://lwn.net/Articles/548500
>
> And, could I know your current progress/schedule? Especially
> when can we see your patches?
>
> Much appreciated!
>
> Thanks,
> Ren
>
> > On 5/20/2013 3:14 AM, Ren Mingxin wrote:
> > > When there is a scsi command timed-out or failed, the scsi eh
> > > tries a thorugh recovery, which is necessary for non-redundant
> > > systems. However, the thorugh recovery usually takes much time,
> > > which is not acceptable for misson critical systems. To improve
> > > this latency, if we are working on a redundant system, we should
> > > avoid the scsi eh for its long time failing recovery, and quick
> > > failover to another path.
> > >
> > > This set of patches is trying to implement above.
> > >
> > > NOTE: the userland tools need to eusure the environment
> > > restriction, which will be implemented later.
> > >
> > > Thanks,
> > > Ren
> > >
> > > Ren Mingxin (5):
> > >    scsi: rename return code FAST_IO_FAIL to FAST_IO
> > >    FC transport: Add interface to specify fast io level for 
> > > timed-out cmds
> > >    SAS transport: Add interface to specify fast io level for 
> > > timed-out cmds
> > >    lpfc: Allow fast timed-out io recovery
> > >    mptfusion: Allow fast timed-out io recovery
> > >
> > >   drivers/message/fusion/mptscsih.c   |   29 ++++++++-
> > >   drivers/scsi/lpfc/lpfc_scsi.c       |   34 ++++++++++
> > >   drivers/scsi/scsi_error.c           |   18 ++---
> > >   drivers/scsi/scsi_sas_internal.h    |    4 -
> > >   drivers/scsi/scsi_transport_fc.c    |  112 
> > > ++++++++++++++++++++++++++++++++++--
> > >   drivers/scsi/scsi_transport_iscsi.c |    6 -
> > >   drivers/scsi/scsi_transport_sas.c   |  103 
> > > ++++++++++++++++++++++++++++++++-
> > >   include/scsi/scsi.h                 |    2
> > >   include/scsi/scsi_transport_fc.h    |   11 +++
> > >   include/scsi/scsi_transport_sas.h   |    8 ++
> > >   10 files changed, 303 insertions(+), 24 deletions(-)
> --
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