| Message ID | 1449788029-23093-1-git-send-email-ukrishn@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 12/10/2015 4:53 PM, Uma Krishnan wrote: > From: "Matthew R. Ochs" <mrochs@linux.vnet.ibm.com> > To remedy this scenario, provide feedback back to the application on > virtual LUN creation as to which ports the LUN may be accessed. LUN's > spanning both ports are candidates for a retry in a presence of an I/O > failure. > > Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com> Acked-by: Manoj Kumar <manoj@linux.vnet.ibm.com> -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> Virtual LUNs may be accessed through one or both ports of the adapter. Is it possible that there might ever be adapters with a number of ports other than 2? In particular, is it possible for 3 or 4 port adapters to exist? If so, do you need something with a bit more fidelity? If not, this is a good approach. Regards, Daniel > This access is encoded in the translation entries that comprise the > virtual LUN and used by the AFU for load-balancing I/O and handling > failover scenarios. In a link loss scenario, even though the AFU is > able to maintain connectivity to the LUN, it is up to the application > to retry the failed I/O. When applications are unaware of the virtual > LUN's underlying topology, they are unable to make a sound decision of > when to retry an I/O and therefore are forced to make their reaction to > a failed I/O absolute. The result is either a failure to retry I/O or > increased latency for scenarios where a retry is pointless. > > To remedy this scenario, provide feedback back to the application on > virtual LUN creation as to which ports the LUN may be accessed. LUN's > spanning both ports are candidates for a retry in a presence of an I/O > failure. > > Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com> > --- > drivers/scsi/cxlflash/vlun.c | 2 ++ > include/uapi/scsi/cxlflash_ioctl.h | 10 ++++++++++ > 2 files changed, 12 insertions(+) > > diff --git a/drivers/scsi/cxlflash/vlun.c b/drivers/scsi/cxlflash/vlun.c > index a53f583..50f8e93 100644 > --- a/drivers/scsi/cxlflash/vlun.c > +++ b/drivers/scsi/cxlflash/vlun.c > @@ -1008,6 +1008,8 @@ int cxlflash_disk_virtual_open(struct scsi_device *sdev, void *arg) > virt->last_lba = last_lba; > virt->rsrc_handle = rsrc_handle; > > + if (lli->port_sel == BOTH_PORTS) > + virt->hdr.return_flags |= DK_CXLFLASH_ALL_PORTS_ACTIVE; > out: > if (likely(ctxi)) > put_context(ctxi); > diff --git a/include/uapi/scsi/cxlflash_ioctl.h b/include/uapi/scsi/cxlflash_ioctl.h > index 831351b..2302f3c 100644 > --- a/include/uapi/scsi/cxlflash_ioctl.h > +++ b/include/uapi/scsi/cxlflash_ioctl.h > @@ -31,6 +31,16 @@ struct dk_cxlflash_hdr { > }; > > /* > + * Return flag definitions available to all ioctls > + * > + * Similar to the input flags, these are grown from the bottom-up with the > + * intention that ioctl-specific return flag definitions would grow from the > + * top-down, allowing the two sets to co-exist. While not required/enforced > + * at this time, this provides future flexibility. > + */ > +#define DK_CXLFLASH_ALL_PORTS_ACTIVE 0x0000000000000001ULL > + > +/* > * Notes: > * ----- > * The 'context_id' field of all ioctl structures contains the context > -- > 2.1.0 > > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@lists.ozlabs.org > https://lists.ozlabs.org/listinfo/linuxppc-dev
On 12/10/2015 4:53 PM, Uma Krishnan wrote: > From: "Matthew R. Ochs" <mrochs@linux.vnet.ibm.com> > > Applications which use virtual LUN's that are backed by a physical LUN > over both adapter ports may experience an I/O failure in the event of > a link loss (e.g. cable pull). > > Virtual LUNs may be accessed through one or both ports of the adapter. > This access is encoded in the translation entries that comprise the > virtual LUN and used by the AFU for load-balancing I/O and handling > failover scenarios. In a link loss scenario, even though the AFU is > able to maintain connectivity to the LUN, it is up to the application > to retry the failed I/O. When applications are unaware of the virtual > LUN's underlying topology, they are unable to make a sound decision of > when to retry an I/O and therefore are forced to make their reaction to > a failed I/O absolute. The result is either a failure to retry I/O or > increased latency for scenarios where a retry is pointless. > > To remedy this scenario, provide feedback back to the application on > virtual LUN creation as to which ports the LUN may be accessed. LUN's > spanning both ports are candidates for a retry in a presence of an I/O > failure. > > Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com> > --- Reviewed-by: Uma Krishnan <ukrishn@linux.vnet.ibm.com> -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/scsi/cxlflash/vlun.c b/drivers/scsi/cxlflash/vlun.c index a53f583..50f8e93 100644 --- a/drivers/scsi/cxlflash/vlun.c +++ b/drivers/scsi/cxlflash/vlun.c @@ -1008,6 +1008,8 @@ int cxlflash_disk_virtual_open(struct scsi_device *sdev, void *arg) virt->last_lba = last_lba; virt->rsrc_handle = rsrc_handle; + if (lli->port_sel == BOTH_PORTS) + virt->hdr.return_flags |= DK_CXLFLASH_ALL_PORTS_ACTIVE; out: if (likely(ctxi)) put_context(ctxi); diff --git a/include/uapi/scsi/cxlflash_ioctl.h b/include/uapi/scsi/cxlflash_ioctl.h index 831351b..2302f3c 100644 --- a/include/uapi/scsi/cxlflash_ioctl.h +++ b/include/uapi/scsi/cxlflash_ioctl.h @@ -31,6 +31,16 @@ struct dk_cxlflash_hdr { }; /* + * Return flag definitions available to all ioctls + * + * Similar to the input flags, these are grown from the bottom-up with the + * intention that ioctl-specific return flag definitions would grow from the + * top-down, allowing the two sets to co-exist. While not required/enforced + * at this time, this provides future flexibility. + */ +#define DK_CXLFLASH_ALL_PORTS_ACTIVE 0x0000000000000001ULL + +/* * Notes: * ----- * The 'context_id' field of all ioctl structures contains the context