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To make use of Jens Axboe's bounce buffer patch, the ServeRAID device
driver
(based on the 2.4.5 kernel) was modified in the following way:

(1) Add "can_dma_32:1" in ips.h to indicate its capability of 32-bit DMA;

(2) Use pci_map_sg to get the dma address of the I/O operations. The
existing 2.4.5 code for pci_map_sg only performs a simple direction
check. The new code added by Jens computes the dma address of the I/O
operations;

(3) For the mapping of the scatter-gather buffers from the SCSI command
to the ServeRAID command, use sg_dma_address to get the dma address
instead of using VIRT_TO_BUS.

With these three changes and Jens' bounce buffer patch, we observed a
significant performance gain for a database workload running on a 4-way
machine. The total elapsed time for processing the queries was cut by 40%.

Jens added that pci_map_page could be used depending on the way the device
driver is written.

The device drivers under drivers/block were modified differently by Jens.
You can examine the changes for cciss and cpqarray for modifying your
own driver.

Jens's bounce buffer patch for 2.4.5 is block-highmem-all-4.gz at
http://www.kernel.org/pub/linux/kernel/people/axboe/patches/2.4.5.


The IPS patch is attached here:

-----------------------------------------------------------------------------------------
--- linux/drivers/scsi/ips.c Sun Aug 19 08:09:14 2001
+++ linux_ips/drivers/scsi/ips.c Sun Aug 19 08:11:33 2001
@@ -3741,8 +3741,11 @@
if (SC->use_sg) {
struct scatterlist *sg;
int i;
+ int tmp;

sg = SC->request_buffer;
+ tmp = pci_map_sg(ha->pcidev, sg, SC->use_sg,
+ ips_command_direction[scb->scsi_cmd->cmnd[0]]);

if (SC->use_sg == 1) {
if (sg[0].length > ha->max_xfer) {
@@ -3752,12 +3755,12 @@
scb->data_len = sg[0].length;

scb->dcdb.transfer_length = scb->data_len;
- scb->data_busaddr = VIRT_TO_BUS(sg[0].address);
+ scb->data_busaddr = sg_dma_address(&sg[0]);
scb->sg_len = 0;
} else {
/* Check for the first Element being bigger than MAX_XFER */
if (sg[0].length > ha->max_xfer) {
- scb->sg_list[0].address = VIRT_TO_BUS(sg[0].address);
+ scb->sg_list[0].address = sg_dma_address(&sg[0]);
scb->sg_list[0].length = ha->max_xfer;
scb->data_len = ha->max_xfer;
scb->breakup = 0;
@@ -3766,7 +3769,7 @@
}
else {
for (i = 0; i < SC->use_sg; i++) {
- scb->sg_list[i].address = VIRT_TO_BUS(sg[i].address);
+ scb->sg_list[i].address = sg_dma_address(&sg[i]);
scb->sg_list[i].length = sg[i].length;

if (scb->data_len + sg[i].length > ha->max_xfer) {
@@ -4441,11 +4444,11 @@
if (sg[0].length - (bk_save * ha->max_xfer)) {
/* Further breakup required */
scb->data_len = ha->max_xfer;
- scb->data_busaddr = VIRT_TO_BUS(sg[0].address + (bk_save * ha->max_xfer));
+ scb->data_busaddr = sg_dma_address(&sg[0]) + (bk_save * ha->max_xfer);
scb->breakup = bk_save + 1;
} else {
scb->data_len = sg[0].length - (bk_save * ha->max_xfer);
- scb->data_busaddr = VIRT_TO_BUS(sg[0].address + (bk_save * ha->max_xfer));
+ scb->data_busaddr = sg_dma_address(&sg[0]) + (bk_save * ha->max_xfer);
}

scb->dcdb.transfer_length = scb->data_len;
@@ -4462,7 +4465,7 @@
/* pointed to by bk_save */
if (scb->sg_break) {
scb->sg_len = 1;
- scb->sg_list[0].address = VIRT_TO_BUS(sg[bk_save].address+ha->max_xfer*scb->sg_break);
+ scb->sg_list[0].address = sg_dma_address(&sg[bk_save])+ha->max_xfer*scb->sg_break;
if (ha->max_xfer > sg[bk_save].length-ha->max_xfer * scb->sg_break)
scb->sg_list[0].length = sg[bk_save].length-ha->max_xfer * scb->sg_break;
else
@@ -4480,7 +4483,7 @@
} else {
/* ( sg_break == 0 ), so this is our first look at a new sg piece */
if (sg[bk_save].length > ha->max_xfer) {
- scb->sg_list[0].address = VIRT_TO_BUS(sg[bk_save].address);
+ scb->sg_list[0].address = sg_dma_address(&sg[bk_save]);
scb->sg_list[0].length = ha->max_xfer;
scb->breakup = bk_save;
scb->sg_break = 1;
@@ -4493,7 +4496,7 @@
scb->sg_break = 0;
/* We're only doing full units here */
for (i = bk_save; i < scb->scsi_cmd->use_sg; i++) {
- scb->sg_list[i - bk_save].address = VIRT_TO_BUS(sg[i].address);
+ scb->sg_list[i - bk_save].address = sg_dma_address(&sg[i]);
scb->sg_list[i - bk_save].length = sg[i].length;
if (scb->data_len + sg[i].length > ha->max_xfer) {
scb->breakup = i; /* sneaky, if not more work, than breakup is 0 */
@@ -4559,6 +4562,9 @@
default:
break;
} /* end case */
+
+ pci_unmap_sg(ha->pcidev, scb->sg_list, scb->scsi_cmd->use_sg,
+ ips_command_direction[scb->scsi_cmd->cmnd[0]]);

return ;
}
--- linux/drivers/scsi/ips.h Sun Aug 19 08:09:19 2001
+++ linux_ips/drivers/scsi/ips.h Sun Aug 19 08:11:47 2001
@@ -419,7 +419,8 @@
present : 0, \
unchecked_isa_dma : 0, \
use_clustering : ENABLE_CLUSTERING, \
- use_new_eh_code : 1 \
+ use_new_eh_code : 1, \
+ can_dma_32 : 1 \
}
#endif
-----------------------------------------------------------------------------------------
Wai Yee Peter Wong
IBM Linux Technology Center, Performance Analysis
email: wpeter@us.ibm.com
Office: (512) 838-9272, T/L 678-9272; Fax: (512) 838-4663

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