On Mon, Jan 10, 2011 at 07:41:22PM +1100, Dave Chinner wrote:
> On Mon, Jan 10, 2011 at 08:57:52AM +0100, Michael Monnerie wrote:
> > On Montag, 10. Januar 2011 Dave Chinner wrote:
> > > This patch uses 32-way threading which results in no noticable
> > > slowdown on single SATA drives with NCQ, but results in ~10x
> > > reduction in runtime on a 12 disk RAID-0 array.
> > Is the fixed 32-way number reasonable, or shouldn't that be "number of
> > available cpu cores"-way? Why threading when you have a single core cpu?
> Sure, 32-way is reasonable on a single disk and CPU. Pretty much
> every sata disk supports NCQ these days, and default to a depth of
> 32, which means we can have 32 concurrent reads in progress at once.
> Phase 2 is all synchronous IO, so the only way to hide the IO
> latency is to queue work to multiple threads and switch between the
> threadsto work on another queue when the current one blocks waiting
> for IO.
The default queue depth for ATA NCQ actually is 31, not 32 for some odd