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.

quoted

+	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)
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