This patch configures the HDD cache for optimal performance even during raw block I/O to and from the block device. This patch does NOT introduce any regression for file-system read/writes.

optimise-sata-raw-block-io-speed

From a5ba7f15275fb43818727e5c735e593a32fe7c89 Mon Sep 17 00:00:00 2001
From: Chinmay V S <cvs268@gmail.com>
Date: Fri, 6 Jul 2012 16:39:37 +0530
Subject: [PATCH] Enable maximum HDD throughput during raw blk I/O.

This patch configures the HDD cache for optimal performance even during
raw block I/O to and from the block device. This patch does NOT
introduce any regression for file-system read/writes.

Signed-off-by: Chinmay V S <cvs268@gmail.com>
---
 drivers/ata/libahci.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index f20c4c9..e091df9 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -72,6 +72,8 @@ static unsigned int ahci_qc_issue(struct ata_queued_cmd *qc);
 static bool ahci_qc_fill_rtf(struct ata_queued_cmd *qc);
 static int ahci_port_start(struct ata_port *ap);
 static void ahci_port_stop(struct ata_port *ap);
+static unsigned int ahci_dummy_read_id(struct ata_device *adev,
+                                struct ata_taskfile *tf, u16 *id);
 static void ahci_qc_prep(struct ata_queued_cmd *qc);
 static int ahci_pmp_qc_defer(struct ata_queued_cmd *qc);
 static void ahci_freeze(struct ata_port *ap);
@@ -174,6 +178,7 @@ struct ata_port_operations ahci_ops = {
 #endif
 	.port_start		= ahci_port_start,
 	.port_stop		= ahci_port_stop,
+	.read_id		= ahci_dummy_read_id,
 };
 EXPORT_SYMBOL_GPL(ahci_ops);
 
@@ -2046,6 +2053,23 @@ static void ahci_port_stop(struct ata_port *ap)
 		ata_port_printk(ap, KERN_WARNING, "%s (%d)\n", emsg, rc);
 }
 
+static unsigned int ahci_dummy_read_id(struct ata_device *adev,
+                                struct ata_taskfile *tf, u16 *id)
+{
+        unsigned int err_mask;
+        unsigned char model_num[ATA_ID_PROD_LEN + 1];
+
+        err_mask = ata_do_dev_read_id(adev, tf, id);
+        if (err_mask)
+                return err_mask;
+
+        id[83] &= ~(1 << 12);   /* Cache flush */
+        id[83] &= ~(1 << 13);   /* LBA48 flush */
+        id[85] &= ~(1 << 5);    /* Write cache */
+
+        return err_mask;
+}
+
 void ahci_print_info(struct ata_host *host, const char *scc_s)
 {
 	struct ahci_host_priv *hpriv = host->private_data;
-- 
1.7.5.4