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Subject[RFC] support for large I/O requests
From
Date

On some system (DDN, for example), we've observed noticable
performance improvement using large I/O requests (1,2,4 MBs).
please, review the patch for inclusion.

thanks, Alex


Signed-off-by: Johann Lombardi <johann.lombardi@bull.net>

Index: linux-2.6.16/include/linux/blkdev.h
===================================================================
--- linux-2.6.16.orig/include/linux/blkdev.h 2006-02-07 14:27:53.000000000 +0100
+++ linux-2.6.16/include/linux/blkdev.h 2006-02-07 15:21:48.000000000 +0100
@@ -667,10 +667,29 @@ extern long blk_congestion_wait(int rw,
extern void blk_rq_bio_prep(request_queue_t *, struct request *, struct bio *);
extern int blkdev_issue_flush(struct block_device *, sector_t *);

-#define MAX_PHYS_SEGMENTS 128
-#define MAX_HW_SEGMENTS 128
#define SAFE_MAX_SECTORS 255
#define BLK_DEF_MAX_SECTORS 1024
+#ifdef CONFIG_LARGE_IO_SIZE_512K
+#define MAX_PHYS_SEGMENTS (1 << (19 - PAGE_CACHE_SHIFT))
+#define MAX_HW_SEGMENTS (1 << (19 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_1M
+#define MAX_PHYS_SEGMENTS (1 << (20 - PAGE_CACHE_SHIFT))
+#define MAX_HW_SEGMENTS (1 << (20 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_2M
+#define MAX_PHYS_SEGMENTS (1 << (21 - PAGE_CACHE_SHIFT))
+#define MAX_HW_SEGMENTS (1 << (21 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_4M
+#define MAX_PHYS_SEGMENTS (1 << (22 - PAGE_CACHE_SHIFT))
+#define MAX_HW_SEGMENTS (1 << (22 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_8M
+#define MAX_PHYS_SEGMENTS (1 << (23 - PAGE_CACHE_SHIFT))
+#define MAX_HW_SEGMENTS (1 << (23 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_16M
+#define MAX_PHYS_SEGMENTS (1 << (24 - PAGE_CACHE_SHIFT))
+#define MAX_HW_SEGMENTS (1 << (24 - PAGE_CACHE_SHIFT))
+#else
+#error "unknown size, check .config"
+#endif

#define MAX_SEGMENT_SIZE 65536

Index: linux-2.6.16/include/linux/bio.h
===================================================================
--- linux-2.6.16.orig/include/linux/bio.h 2006-02-07 14:27:53.000000000 +0100
+++ linux-2.6.16/include/linux/bio.h 2006-02-07 15:22:35.000000000 +0100
@@ -46,7 +46,22 @@
#define BIO_BUG_ON
#endif

-#define BIO_MAX_PAGES (256)
+#ifdef CONFIG_LARGE_IO_SIZE_512K
+#define BIO_MAX_PAGES (1 << (19 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_1M
+#define BIO_MAX_PAGES (1 << (20 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_2M
+#define BIO_MAX_PAGES (1 << (21 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_4M
+#define BIO_MAX_PAGES (1 << (22 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_8M
+#define BIO_MAX_PAGES (1 << (23 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_16M
+#define BIO_MAX_PAGES (1 << (24 - PAGE_CACHE_SHIFT))
+#else
+#error "unknown size, check .config"
+#endif
+
#define BIO_MAX_SIZE (BIO_MAX_PAGES << PAGE_CACHE_SHIFT)
#define BIO_MAX_SECTORS (BIO_MAX_SIZE >> 9)

Index: linux-2.6.16/include/scsi/scsi_host.h
===================================================================
--- linux-2.6.16.orig/include/scsi/scsi_host.h 2006-02-07 14:27:53.000000000 +0100
+++ linux-2.6.16/include/scsi/scsi_host.h 2006-02-07 15:20:30.000000000 +0100
@@ -25,7 +25,21 @@ struct scsi_transport_template;
* used in one scatter-gather request.
*/
#define SG_NONE 0
-#define SG_ALL 0xff
+#ifdef CONFIG_LARGE_IO_SIZE_512K
+#define SG_ALL (1 << (19 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_1M
+#define SG_ALL (1 << (20 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_2M
+#define SG_ALL (1 << (21 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_4M
+#define SG_ALL (1 << (22 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_8M
+#define SG_ALL (1 << (23 - PAGE_CACHE_SHIFT))
+#elif CONFIG_LARGE_IO_SIZE_16M
+#define SG_ALL (1 << (24 - PAGE_CACHE_SHIFT))
+#else
+#error "unknown size, check .config"
+#endif


#define DISABLE_CLUSTERING 0
Index: linux-2.6.16/drivers/block/Kconfig
===================================================================
--- linux-2.6.16.orig/drivers/block/Kconfig 2006-02-07 14:28:10.000000000 +0100
+++ linux-2.6.16/drivers/block/Kconfig 2006-02-07 15:28:41.000000000 +0100
@@ -461,6 +461,30 @@ config LBD
your machine, or if you want to have a raid or loopback device
bigger than 2TB. Otherwise say N.

+choice
+ prompt "Support for Large I/O Requests"
+ default LARGE_IO_SIZE_512K
+
+config LARGE_IO_SIZE_512K
+ bool "512K"
+
+config LARGE_IO_SIZE_1M
+ bool "1M"
+
+config LARGE_IO_SIZE_2M
+ bool "2M"
+
+config LARGE_IO_SIZE_4M
+ bool "4M"
+
+config LARGE_IO_SIZE_8M
+ bool "8M"
+
+config LARGE_IO_SIZE_16M
+ bool "16M"
+
+endchoice
+
config CDROM_PKTCDVD
tristate "Packet writing on CD/DVD media"
depends on !UML
Index: linux-2.6.16/drivers/scsi/scsi_lib.c
===================================================================
--- linux-2.6.16.orig/drivers/scsi/scsi_lib.c 2006-02-07 14:27:53.000000000 +0100
+++ linux-2.6.16/drivers/scsi/scsi_lib.c 2006-02-07 17:24:17.000000000 +0100
@@ -55,11 +55,23 @@ struct scsi_host_sg_pool scsi_sg_pools[]
#if (SCSI_MAX_PHYS_SEGMENTS > 128)
SP(256),
#if (SCSI_MAX_PHYS_SEGMENTS > 256)
+ SP(512),
+#if (SCSI_MAX_PHYS_SEGMENTS > 512)
+ SP(1024),
+#if (SCSI_MAX_PHYS_SEGMENTS > 1024)
+ SP(2048),
+#if (SCSI_MAX_PHYS_SEGMENTS > 2048)
+ SP(4096),
+#if (SCSI_MAX_PHYS_SEGMENTS > 4096)
#error SCSI_MAX_PHYS_SEGMENTS is too large
#endif
#endif
#endif
#endif
+#endif
+#endif
+#endif
+#endif
};
#undef SP

-
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