On Dec 10, 2007 6:37 PM, Jens Axboe <[EMAIL PROTECTED]> wrote: > > On Mon, Dec 10 2007, jidong xiao wrote: > > Hi, > > > > I am reading the source code of block I/O layer, and now seeing there > > saying "ordering by draining" or "ordering by tag" in > > include/blkdev.h,and the comments in that file says: "Hardbarrier is > > supported with one of the following methods", but what do these two > > methods exactly mean? > > ordering by draining means that you empty the pending queue of requests > and then flush the cache to prevent a later issue of a new request to > reach the platter before the older ones. order by tag means that the hw > has a way of being told not to reorder beyond the barrier, in which case > you don't have to drain the queue. >
Well, I saw these comments in sd_revalidate_disk(), does this mean SCSI TCQ is not supported in Linux? 1545 /* 1546 * We now have all cache related info, determine how we deal 1547 * with ordered requests. Note that as the current SCSI 1548 * dispatch function can alter request order, we cannot use 1549 * QUEUE_ORDERED_TAG_* even when ordered tag is supported. 1550 */ 1551 if (sdkp->WCE) 1552 ordered = sdkp->DPOFUA 1553 ? QUEUE_ORDERED_DRAIN_FUA : QUEUE_ORDERED_DRAIN_FLUSH; 1554 else 1555 ordered = QUEUE_ORDERED_DRAIN; 1556 1557 blk_queue_ordered(sdkp->disk->queue, ordered, sd_prepare_flush); Regards Jason -- 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/
