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@xxxxxxxxxxx ------- The Corporate Village, Da Vincilaan 7-D1
Voice +32-2-7008453 Fax +32-2-7008622 ---------------- B-1935 Zaventem, Belgium
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