2.4.x swim3 performance problem on PM4400 identified

[Benjamin Herrenschmidt]

On Fri, 2003-03-28 at 16:40, Mikael Pettersson wrote:
> With 2.4 kernels, writes to floppy are about a factor of 10 slower
> on my PowerMac 4400 than they are with 2.2 kernels.
>
> The cause for this is a poll-loop in swim3.c which doesn't exist
> in the 2.2 version. The patch below reverts that change, and
> restores floppy write performance to 2.2 levels. I've built many
> boot floppies with this modified driver w/o any problems.

That's interesting. I'll look into more details and post
a patch for my next -ben kernel release. Thanks for taking
the time to investigate.

> --- linux-2.4.21-pre6/drivers/block/swim3.c.~1~	Wed Aug  7 00:52:20 2002
> +++ linux-2.4.21-pre6/drivers/block/swim3.c	Fri Mar 28 16:02:17 2003
> @@ -679,10 +679,14 @@
>  			break;
>  		dr = fs->dma;
>  		cp = fs->dma_cmd;
> +#if 0	/* This causes massive performance problems for my PM4400. /Mikael */
>  		/* We must wait a bit for dbdma to complete */
>  		for (n=0; (in_le32(&dr->status) & ACTIVE) && n < 1000; n++)
>  			udelay(10);
>  		DBDMA_DO_STOP(dr);
> +#else	/* This is from 2.2 and it works much better for my PM4400. /Mikael */
> +		st_le32(&dr->control, RUN << 16);
> +#endif
>  		out_8(&sw->intr_enable, 0);
>  		out_8(&sw->control_bic, WRITE_SECTORS | DO_ACTION);
>  		out_8(&sw->select, RELAX);
>
--
Benjamin Herrenschmidt <benh at kernel.crashing.org>

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