Re: Marvell MV88SX6041 SATA Driver PIO4 Mode Not DMA

[Jens Axboe <axboe@suse.de>]

On Fri, Nov 11 2005, Jens Axboe wrote:
> On Fri, Nov 11 2005, Jeff Garzik wrote:
> > Jens Axboe wrote:
> > >On Fri, Nov 11 2005, Jeff Garzik wrote:
> > >
> > >>Spencer Tuttle wrote:
> > >>
> > >>>I have just compiled the new 2.6.14 kernel from the gentoo-sources tree.
> > >>>
> > >>>I can access the drives just fine, but it seems really slow.  Here is
> > >>>the dmesg output when I load the kernel module
> > >>
> > >>That's expected, since the driver in 2.6.14 only does PIO mode.
> > >>
> > >>Try 2.6.14-gitN which supports EDMA.
> > >
> > >
> > >Did you see these as well:
> > >
> > >blk_queue_max_hw_segments: set to minimum 1
> > >
> > >Could it be forgetting to set ->sg_tablesize as well?
> > 
> > [jgarzik@sata linux-2.6]$ grep MV_MAX_SG_CT drivers/scsi/sata_mv.c
> >         MV_MAX_SG_CT            = 176,
> >         MV_SG_TBL_SZ            = (16 * MV_MAX_SG_CT),
> >         .sg_tablesize           = MV_MAX_SG_CT,
> 
> It was just a guess, clearly someone is calling scsi_alloc_queue() with
> an sdev->host->sg_tablesize of 0. While that wont make PIO a whole lot
> faster, it's clearly a bug and would certainly hurt DMA performance.

Before commit 31961943e3110c5a1c36b1e0069c29f7c4380e51, sata_mv had
->sg_tablesize set to MV_UNDEF which was defined to 0. Just checking,
2.6.14 ships with that.

-- 
Jens Axboe