On 12-08-07 01:16 PM, Mark Lord wrote: .. > mv_wait_for_edma_empty_idle() is called from mv_stop_edma(), > which happens whenever we transition between sending NCQ commands > (eg. read/write) and non-NCQ commands (eg. flush cache). > > The mv_qc_defer() function is supposed to ensure that things are > more or less idle before it even gets to mv_stop_edma(). > So we'd expect the mv_wait_for_edma_empty_idle() function to be quick, > which is a big part of why we're willing to tolerate an inline busy-wait. > > But here it seems to be waiting MUCH longer, as if it has to wait for > some IO-in-progress to complete before continuing. Which means that > the mv_qc_defer() function isn't being as effective as it should be. > > The idea is, before any new command is queued, libata invokes the defer > function to see if the driver is ready to accept the new command. > The sata_mv driver normally says "yes" (go ahead) for a new NCQ command > whenever it currently has existing NCQ commands in-flight. > Otherwise it always says "no" (please defer) unless completely idle. > That's how mv_qc_defer() is supposed to work, and that should minimize > the time spent inside mv_wait_for_edma_empty_idle() by ensuring the > edma engine is already idle whenever that gets called. Say, here's a thought: We could get rid of (or relocate to upper layers) the busy-wait by having something similar get called from ata_qc_defer(). If you are feeling adventurous, here is a 100% untested patch to do just that. It looks correct to me, it compiles, but that's all I can say. The attached copy is the better one to use -- my mailer mangles inline patches. --- linux-3.4.4/drivers/ata/sata_mv.c 2012-06-22 14:37:50.000000000 -0400 +++ linux/drivers/ata/sata_mv.c 2012-08-07 14:14:43.554503157 -0400 @@ -1388,6 +1388,17 @@ } } +static int mv_check_for_edma_empty_idle(struct ata_port *ap) +{ + void __iomem *port_mmio = mv_ap_base(ap); + const u32 empty_idle = (EDMA_STATUS_CACHE_EMPTY | EDMA_STATUS_IDLE); + + u32 edma_stat = readl(port_mmio + EDMA_STATUS); + if ((edma_stat & empty_idle) == empty_idle) + return ATA_DEFER_PORT; + return 0; +} + static int mv_qc_defer(struct ata_queued_cmd *qc) { struct ata_link *link = qc->dev->link; @@ -1423,7 +1434,7 @@ * If the port is completely idle, then allow the new qc. */ if (ap->nr_active_links == 0) - return 0; + return mv_check_for_edma_empty_idle(ap); /* * The port is operating in host queuing mode (EDMA) with NCQ
--- linux-3.4.4/drivers/ata/sata_mv.c 2012-06-22 14:37:50.000000000 -0400 +++ linux/drivers/ata/sata_mv.c 2012-08-07 14:14:43.554503157 -0400 @@ -1388,6 +1388,17 @@ } } +static int mv_check_for_edma_empty_idle(struct ata_port *ap) +{ + void __iomem *port_mmio = mv_ap_base(ap); + const u32 empty_idle = (EDMA_STATUS_CACHE_EMPTY | EDMA_STATUS_IDLE); + + u32 edma_stat = readl(port_mmio + EDMA_STATUS); + if ((edma_stat & empty_idle) == empty_idle) + return ATA_DEFER_PORT; + return 0; +} + static int mv_qc_defer(struct ata_queued_cmd *qc) { struct ata_link *link = qc->dev->link; @@ -1423,7 +1434,7 @@ * If the port is completely idle, then allow the new qc. */ if (ap->nr_active_links == 0) - return 0; + return mv_check_for_edma_empty_idle(ap); /* * The port is operating in host queuing mode (EDMA) with NCQ