Re: [PATCH] libsas: Don't issue commands to devices that have been hot-removed.

[Brian King <brking@linux.vnet.ibm.com>]

Darrick J. Wong wrote:
> In general, I agree that sas-ata should adopt the new EH.
> Unfortunately, I believe the old way of sas-ata configuring ATA ports is
> somehow not compatible with the new EH stuff and causes a crash during
> the device probe with my patch to move sas-ata to the new EH.  If I
> apply the patch that migrates sas-ata to use brking's latest ata-sas
> configuration mechanism (the one that creates real ata_hosts), I see
> (a) lots and lots of ATA hosts getting created (one per ATA port;
> possibly undesirable if you've a SAS topology with a lot of SATA disks)

The new libata EH ends up spending more time in the error handling thread
than the old code did. One of the reasons having multiple ATA/SCSI hosts
is a good thing is that is the granularity of error handling, so it
prevents stalling all the other devices under that SAS HBA while we are
hitting errors on an ATAPI SATA device, for example.

Arguably, SATA users of libata already have one SCSI host per ATA port,
so my SAS patches really just bring SAS in line with that design...

-Brian

-- 
Brian King
Linux on Power Virtualization
IBM Linux Technology Center