On Mon, Dec 11 2006, Ming Zhang wrote: > On Mon, 2006-12-11 at 15:50 +0100, Jens Axboe wrote: > > > > > > Linux doesn't guarantee any request ordering for O_DIRECT io. > > > > > > > > > > so this means it can be inserted front and back. and no fixed > > order? > > > > > > > > It'll be sort inserted like any other request. That might be > > front, it > > > > might be back, or it migth be somewhere in the middle. > > > > > > ic, so no special treatment here. > > > > Nope. In fact the block layer and io scheduler do not know that this > > is > > an O_DIRECT request, the bio originates from the same path as any > > other > > regular fs request. > > one more question. since our point to have this block io is to by pass > OS and send to high performance storage target. so if I use NOOP > scheduler here, which simply add request to the tail of queue, then > block io later will preserve the order. will this be ok? even device can > do out of order, but device should do it in a safe way i think...
noop won't reorder requests through insertion sort, but it could potentially still do so for merges. Putting any sort of faith in what a device will or will not do outside of what is mandated by the spec, is not a good plan imho :-) -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-btrace" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
