linux-kernel - Re: [patch 6/7] ps3: ROM Storage Driver

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Date:	Tue, 29 May 2007 13:11:41 +0200 (CEST)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Christoph Hellwig <hch@....de>
cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [patch 6/7] ps3: ROM Storage Driver

On Tue, 29 May 2007, Christoph Hellwig wrote:
> [Note that all scsi lldds should go to linux-scsi]

I'll Cc linux-scsi next time.

> > +	sgpnt = cmd->request_buffer;
> > +	active = 1;
> > +	for (k = 0, req_len = 0, act_len = 0; k < cmd->use_sg; ++k, ++sgpnt) {
> > +		if (active) {
> > +			kaddr = kmap_atomic(sgpnt->page, KM_USER0);
> > +			if (!kaddr)
> > +				return DID_ERROR << 16;
> > +			len = sgpnt->length;
> > +			if ((req_len + len) > buflen) {
> > +				active = 0;
> > +				len = buflen - req_len;
> > +			}
> > +			memcpy(kaddr + sgpnt->offset, buf + req_len, len);
> > +			kunmap_atomic(kaddr, KM_USER0);
> > +			act_len += len;
> > +		}
> > +		req_len += sgpnt->length;
> > +	}
> > +	cmd->resid = req_len - act_len;
> 
> This looks very inefficient.  Just set sg_tablesize of your driver
> to 1 to avoid getting mutiple segments.

The disadvantage of setting sg_tablesize = 1 is that the driver will get small
requests (PAGE_SIZE) most of the time, which is very bad for performance.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- Sony Network and Software Technology Center Europe (NSCE)
Geert.Uytterhoeven@...ycom.com ------- The Corporate Village, Da Vincilaan 7-D1
Voice +32-2-7008453 Fax +32-2-7008622 ---------------- B-1935 Zaventem, Belgium
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