linux-kernel - [PATCH] sata_nv: add a module parameter to enable async scanning

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Message-Id: <1236543237.5783.16.camel@andreas-laptop>
Date:	Sun, 08 Mar 2009 21:13:57 +0100
From:	Andreas Robinson <andr345@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] sata_nv: add a module parameter to enable async scanning

On Sun, 2009-03-08 at 09:01 -0700, Arjan van de Ven wrote:
> One thing to mention is that fastinit for sata... I only did AHCI
> (because all my machines have that). Your machine looks like it has
> something different than AHCI, so maybe the sata controller can use
> some work ;-)
> (a sata driver needs to opt into parallel scanning via a flag)
> 
> SATA init tends to be one of the things that are fix time per drive;
> and so working on that first to at least ONLY get that is worth it,
> it's a huge chunk of time (more than half the total time in your
> bootchart)

Something like the patch below, mabye? :-)

Before: [    3.056308] Freeing unused kernel memory: 364k freed
After:  [    2.411417] Freeing unused kernel memory: 364k freed

The chipset is nforce2 (drivers/ata/sata_nv.c). I couldn't find
anything like the SSS flag documented in the code, and register
specs from nvidia are as rare as hen's teeth... So I only added
the module parameter to force parallel scans.

I named it parallel_scan instead of ignore_sss though, since
there might not be an SSS-flag to ignore.

/Andreas

>>From a5b090856173782308c8f61de84085be9a9b73ba Mon Sep 17 00:00:00 2001
From: Andreas Robinson <andr345@...il.com>
Date: Sun, 8 Mar 2009 20:44:16 +0100
Subject: [PATCH] sata_nv: add a module parameter to enable async scanning

This parameter (parallel_scan) forces the OS to scan for
disks asynchronously/in parallel, to reduce boot time.

It might cause problems (brown-outs, blown fuses) in
multi-drive systems, if the PSU is unable to handle several
drives spinning up simultaneously.

It ought to be safe in single-drive systems.

Signed-off-by: Andreas Robinson <andr345@...il.com>
---
 drivers/ata/sata_nv.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/ata/sata_nv.c b/drivers/ata/sata_nv.c
index 55a8eed..e8aba2f 100644
--- a/drivers/ata/sata_nv.c
+++ b/drivers/ata/sata_nv.c
@@ -579,6 +579,7 @@ MODULE_VERSION(DRV_VERSION);
 
 static int adma_enabled;
 static int swncq_enabled = 1;
+static int parallel_scan = 0;
 
 static void nv_adma_register_mode(struct ata_port *ap)
 {
@@ -2427,6 +2428,9 @@ static int nv_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 	} else if (type == SWNCQ)
 		nv_swncq_host_init(host);
 
+	if (parallel_scan)
+		host->flags |= ATA_HOST_PARALLEL_SCAN;
+
 	pci_set_master(pdev);
 	return ata_host_activate(host, pdev->irq, ipriv->irq_handler,
 				 IRQF_SHARED, ipriv->sht);
@@ -2526,4 +2530,6 @@ module_param_named(adma, adma_enabled, bool, 0444);
 MODULE_PARM_DESC(adma, "Enable use of ADMA (Default: true)");
 module_param_named(swncq, swncq_enabled, bool, 0444);
 MODULE_PARM_DESC(swncq, "Enable use of SWNCQ (Default: true)");
+module_param_named(parallel_scan, parallel_scan, bool, 0444);
+MODULE_PARM_DESC(parallel_scan, "Force parallel host scan (Default: false)");
 
-- 
1.5.6.3


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