On Fri, Apr 27, 2007 at 01:08:17AM +1000, Nick Piggin wrote: > Andy Whitcroft wrote: > >Nick Piggin wrote: > > > > >>I don't understand what you mean at all. A block has always been a > >>contiguous area of disk. > > > > > >Lets take Nick's definition of block being a disk based unit for the > >moment. That does not change the key contention here, that even with > >hardware specifically designed to handle 4k pages that hardware handles > >larger contigious areas more efficiently. David Chinner gives us > >figures showing major overall throughput improvements from (I assume) > >shorter scatter gather lists and better tag utilisation. I am loath to > >say we can just blame the hardware vendors for poor design. > > So their controllers get double the throughput when going from 512K > (128x4K pages) to 2MB (128x16K pages) requests. Do you really think > it is to do with command processing overhead?
No - it has to do with things like the RAID controller caching behaviour, the number of disks a single request can keep busy, getting I/os large enough to avoid partial stripe writes, etc. Remember that this controller is often on the other side of a HBA so large I/Os are really desirable here.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - 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/
