On 2005-04-04T15:48:36, "goggin, edward" <egoggin@xxxxxxx> wrote: > In the interest of reducing delay time when testing either good or > failed paths, could we (1) prevent SCSI mid-layer initiated i/o > retry of these requests and (2) insert the test path i/os at the > head of the path's block i/o queue? Doing either of these will > require some kernel enhancement since there is no way to > either request fail fast capability or insertion at queue head for > a SCSI CDB issued from user space. > > Currently the scsi_cmd_ioctl->sg_io->blk_execute_rq code > path for a multipath test i/o does not set the REQ_FAILFAST > bit in the flags field of the request structure and unconditionally > inserts the request at the tail of the request queue for the scsi > device representing the scsi path being tested. > > Possibly the desire for each of these two attributes could be > passed as a flag bit setting in the flag field of the sg_io_hdr > structure passed into the kernel as part of the test path ioctl(2). Jens: Indeed, being able to inflict the equivalent of BIO_RW_FAILFAST on a raw request from user-space would be desireable. Do you have any objections or suggestions how this could be done best? Mit freundlichen Grüßen, Lars Marowsky-Brée <lmb@xxxxxxx> -- High Availability & Clustering SUSE Labs, Research and Development SUSE LINUX Products GmbH - A Novell Business