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authorMatthew Wilcox <matthew@wil.cx>2008-07-06 09:23:20 -0400
committerJeff Garzik <jgarzik@redhat.com>2008-07-14 15:59:34 -0400
commit2640d7c0b8d5d9d9ee303b8cd09f5124176f6239 (patch)
tree8a3e23cc8c248bd7ea06c2920729d5e82ce0e886
parent24920c8a6358bf5532f1336b990b1c0fe2b599ee (diff)
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 <willy@linux.intel.com> Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
-rw-r--r--drivers/ata/ahci.c1
1 files changed, 0 insertions, 1 deletions
diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 4ff3f03cf97b..dc7596f028b6 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);