[dm-devel] reducing path test delays

[Lars Marowsky-Bree]

On 2005-04-11T08:43:08, Jens Axboe <axboe at suse.de> 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).

Ed, do you have a patch yet?


Sincerely,
    Lars Marowsky-Brée <lmb at suse.de>

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