From: Matthew Wilcox Date: Sun, 6 Jul 2008 13:23:20 +0000 (-0400) Subject: AHCI: Remove an unnecessary flush from ahci_qc_issue X-Git-Tag: v2.6.27-rc1~1076^2 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=2640d7c0b8d5d9d9ee303b8cd09f5124176f6239;p=linux-2.6-omap-h63xx.git AHCI: Remove an unnecessary flush from ahci_qc_issue In an I/O heavy workload (IOZone), ahci_qc_issue is the second-highest consumer of CPU cycles. Removing the flush gets us approximately 10% bandwidth improvement. I believe this to be because the CPU can start queueing the next request instead of waiting for the readl() to flush the writes to the device. The flush isn't necessary because we're using a 'queue' metaphor; we don't guarantee the command has got to the device, nor do we need to guarantee the command has got to the controller. Signed-off-by: Matthew Wilcox Signed-off-by: Jeff Garzik --- diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c index 4ff3f03cf97..dc7596f028b 100644 --- a/drivers/ata/ahci.c +++ b/drivers/ata/ahci.c @@ -2136,7 +2136,6 @@ static unsigned int ahci_qc_issue(struct ata_queued_cmd *qc) if (qc->tf.protocol == ATA_PROT_NCQ) writel(1 << qc->tag, port_mmio + PORT_SCR_ACT); writel(1 << qc->tag, port_mmio + PORT_CMD_ISSUE); - readl(port_mmio + PORT_CMD_ISSUE); /* flush */ ahci_sw_activity(qc->dev->link);