On Thu, Apr 26, 2007 at 01:37:42PM +0100, Andy Whitcroft wrote: > Nick Piggin wrote: > > Christoph Lameter wrote: > >> On Thu, 26 Apr 2007, Nick Piggin wrote: > >>>> What are the exact requirement you are trying to address? > >>> > >>> Block size > page cache size. > >> > >> But what do you mean with it? A block is no longer a contiguous > >> section of memory. So you have redefined the term. > > > > 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 haven't actually provided any figures - it's knowledge passed down from those that know more about it that I do. If you want figures about the impact of large I/Os, then we should not be looking at the HBAs but at the impact on RAID controller throughput (this I do have numbers on ;). It is not uncommon to see 2MB I/Os give twice the throughput of 512K I/Os to a single RAID controller - larger than 512k can only be acheived on systems with a page size larger than 4k..... > I am loath to > say we can just blame the hardware vendors for poor design. Never did - I'm pointing out that linux can't use all the capabilities they have. 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/