From: Jeff Garzik The "lba48" feature in ATA allows for addressing of sectors > 137GB, and also allows for transfers of up to 64K sector, instead of the traditional 256 sectors in older ATA. libata simply limited all transfers to a 200 sectors (just under the 256 sector limit). This was mainly being careful, and making sure I had a solution that worked everywhere. I also wanted to see how the iommu S/G stuff would shake out. Things seem to be looking pretty good, so it's now time to turn on lba48-sized transfers. Most SATA disks will be lba48 anyway, even the ones smaller than 137GB, for this and other reasons. With this simple patch, the max request size goes from 128K to 32MB... so you can imagine this will definitely help performance. Throughput goes up. Interrupts go down. Fun for the whole family. The attached patch is for 2.6.x kernels only. It should apply to 2.6.5-rc2 or later, including my latest 2.6-libata patch on kernel.org. This patch should be pretty harmless, but you never know what could happen when you throw the throttle wide open. Testing in -mm would be a good thing, for example :) Volunteers are welcome to post a 2.4 backport of this patch to linux-ide@vger.kernel.org, and I'll merge it into my 2.4 libata queue. Here's what dmesg looks like on my workstation. Look for the "max request 32MB" message just after SCSI prints out the disk information. libata version 1.02 loaded. ata_piix version 1.02 PCI: Setting latency timer of device 0000:00:1f.2 to 64 ata1: SATA max UDMA/133 cmd 0x24F0 ctl 0x280A bmdma 0x24D0 irq 169 ata2: SATA max UDMA/133 cmd 0x24F8 ctl 0x280E bmdma 0x24D8 irq 169 ata1: dev 0 cfg 49:2f00 82:7c6b 83:7f09 84:4003 85:7c69 86:3e01 87:4003 88:207f ata1: dev 0 ATA, max UDMA/133, 488281250 sectors (lba48) ata1: dev 0 configured for UDMA/133 scsi0 : ata_piix ata2: SATA port has no device. ata2: thread exiting scsi1 : ata_piix Vendor: ATA Model: Maxtor 6Y250M0 Rev: 1.02 Type: Direct-Access ANSI SCSI revision: 05 ata1: dev 0 max request 32MB (lba48) SCSI device sda: 488281250 512-byte hdwr sectors (250000 MB) SCSI device sda: drive cache: write through sda: sda1 Attached scsi disk sda at scsi0, channel 0, id 0, lun 0 Attached scsi generic sg0 at scsi0, channel 0, id 0, lun 0, type 0 --- 25-akpm/drivers/scsi/libata-scsi.c | 17 +++++++++++++++++ 1 files changed, 17 insertions(+) diff -puN drivers/scsi/libata-scsi.c~speed-up-sata drivers/scsi/libata-scsi.c --- 25/drivers/scsi/libata-scsi.c~speed-up-sata 2004-04-15 13:48:53.773655512 -0700 +++ 25-akpm/drivers/scsi/libata-scsi.c 2004-04-15 13:48:53.777654904 -0700 @@ -169,6 +169,23 @@ int ata_scsi_slave_config(struct scsi_de sdev->use_10_for_ms = 1; blk_queue_max_phys_segments(sdev->request_queue, LIBATA_MAX_PRD); + if (sdev->id < ATA_MAX_DEVICES) { + struct ata_port *ap; + struct ata_device *dev; + + ap = (struct ata_port *) &sdev->host->hostdata[0]; + dev = &ap->device[sdev->id]; + + if (dev->flags & ATA_DFLAG_LBA48) { + sdev->host->max_sectors = 65534; + blk_queue_max_sectors(sdev->request_queue, 65534); + printk(KERN_INFO "ata%u: dev %u max request 32MB (lba48)\n", + ap->id, sdev->id); + } else + printk(KERN_INFO "ata%u: dev %u max request 128K\n", + ap->id, sdev->id); + } + return 0; /* scsi layer doesn't check return value, sigh */ } _