On Mon, 2005-01-24 at 13:49 -0200, Marcelo Tosatti wrote: > So is it valid to affirm that on average an operation with one SG element > pointing to a 1MB > region is similar in speed to an operation with 16 SG elements each pointing > to a 64K > region due to the efficient onboard SG processing?
it's within a few percent, yes. And the figures depend on how good the I/O card is at it. I can imagine there are some wildly varying I/O cards out there. However, also remember that 1MB of I/O is getting beyond what's sensible for a disc device anyway. The cable speed is much faster than the platter speed, so the device takes the I/O into its cache as it services it. If you overrun the cache it will burp (disconnect) and force a reconnection to get the rest (effectively splitting the I/O up anyway). This doesn't apply to arrays with huge caches, but it does to pretty much everything else. The average disc cache size is only a megabyte or so. James - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
