qemu-sh CF access perormance

DISCUSSION Shin-ichiro KAWASAKI 3 participants 5 messages Mar 31, 2009 – Apr 2, 2009

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Shin-ichiro KAWASAKI

author

2009-03-31 13:19 UTC #0 lore raw

Hi. I have a question related to qemu-sh.

I use qemu-sh r2d emulation and userland on compact flush as qemu disk image, to investigate why qemu-sh system emulation is slower than qemu-arm.

For example, it takes only around 1 second to compile simple hello.c with gcc on qemu-arm system emulation. On the other hand, it takes around 40 seconds on qemu-sh system emulation.

This compile time (40 secs) reduces to less than 6 seconds, if I repeat to invoke "% gcc hello.c". Then I guess,

- disk cache reduces the compile time
- and compact flush access performance is rather bad on qemu-sh r2d system

I investigated what happens on CF access, and found

- the ioread/write16_rep() function call in ata_sff_data_xfer() placed in "drivers/ata/libata-sff.c", cause tlb miss exception,

- and the exception is handled by handle_trapped_io() in "arch/sh/kernel/io_trapped.c".

I'd like to ask following questions to linux-sh experts,

- Why such io-traps are used to access CF?
- Will this io-traps are used for SH7785LCR's SD card access?

I guess these io-traps can be the reason why gcc takes so much time on qemu-sh.

Thank you for reading this mail.
Any comments or any explanations will be appreciated.

Regards,
Shin-ichiro KAWASAKI

Magnus Damm

2009-04-01 04:22 UTC #1 lore raw

2009/3/31 Shin-ichiro KAWASAKI <[email protected]>:

Quoted 6 lines

I'd like to ask following questions to linux-sh experts,
- Why such io-traps are used to access CF?
- Will this io-traps are used for SH7785LCR's SD card access?
I guess these io-traps can be the reason why gcc takes so much time on qemu-sh.

The r2d hardware implements 16-bit only CF interface while driver software requires 8-bit access. To work around this issue io_trapped is used to convert 8-bit accesses to 16-bit accesses. This is quite slow.

For more information, please see the comment in arch/sh/boards/mach-r2d/setup.c

To improve performance, consider adding a command line flag to the kernel that disables io_trapped. This flag can then be set on the kernel command line by the person running qemu.

Hope this helps!

Cheers,

/ magnus

Shin-ichiro KAWASAKI

author

2009-04-01 15:25 UTC #2 lore raw

In reply to Shin-ichiro KAWASAKI

Hi, Magnus! Thank you for your explanation.

Quoted 13 lines · Magnus Damm

2009/3/31 Shin-ichiro KAWASAKI <[email protected]>:
Quoted 6 lines
I'd like to ask following questions to linux-sh experts,
- Why such io-traps are used to access CF?
- Will this io-traps are used for SH7785LCR's SD card access?
I guess these io-traps can be the reason why gcc takes so much time on qemu-sh.
The r2d hardware implements 16-bit only CF interface while driver software requires 8-bit access. To work around this issue io_trapped is used to convert 8-bit accesses to 16-bit accesses. This is quite slow.

Quoted 7 lines

For more information, please see the comment in arch/sh/boards/mach-r2d/setup.c
To improve performance, consider adding a command line flag to the kernel that disables io_trapped. This flag can then be set on the kernel command line by the person running qemu.
Hope this helps!

It really helps!

The attached patch is a rough implementation to add a command line flag 'avoid_trap', which Magnus suggested. It is just a reference, but it reduces the gcc compile time from 40 seconds to around 4 seconds. 10 times faster!

Is it OK to add such qemu specific options to linux kernel mainline?

Regards,
Shin-ichiro KAWASAKI

linux-2.6.28/arch/sh/boards/mach-r2d/setup.c +6 -1

@@ -198,9 +198,11 @@
 	.minimum_bus_width	= 16,
 };
 
+static int avoid_trap;
+
 static int __init rts7751r2d_devices_setup(void)
 {
-	if (register_trapped_io(&cf_trapped_io) = 0)
+	if (avoid_trap || register_trapped_io(&cf_trapped_io) = 0)
 		platform_device_register(&cf_ide_device);
 
 	spi_register_board_info(spi_bus, ARRAY_SIZE(spi_bus));

@@ -245,6 +247,9 @@
 
 	sm501_reg = (void __iomem *)0xb3e00000 + SM501_DRAM_CONTROL;
 	writel(readl(sm501_reg) | 0x00f107c0, sm501_reg);
+
+    if (strstr(*cmdline_p, "avoid_trap"))
+        avoid_trap = 1;
 }
 
 /*

Paul Mundt

2009-04-02 03:32 UTC #3 lore raw

In reply to Shin-ichiro KAWASAKI

Quoted 26 lines · Shin-ichiro KAWASAKI

Hi, Magnus! Thank you for your explanation.
Quoted 14 lines · Magnus Damm
2009/3/31 Shin-ichiro KAWASAKI <[email protected]>:
Quoted 7 lines
I'd like to ask following questions to linux-sh experts,
- Why such io-traps are used to access CF?
- Will this io-traps are used for SH7785LCR's SD card access?
I guess these io-traps can be the reason why gcc takes so much time on qemu-sh.
The r2d hardware implements 16-bit only CF interface while driver software requires 8-bit access. To work around this issue io_trapped is used to convert 8-bit accesses to 16-bit accesses. This is quite slow.
Quoted 8 lines
For more information, please see the comment in
arch/sh/boards/mach-r2d/setup.c
To improve performance, consider adding a command line flag to the kernel that disables io_trapped. This flag can then be set on the kernel command line by the person running qemu.
Hope this helps!

Quoted 9 lines

It really helps!
The attached patch is a rough implementation to add a command line flag 'avoid_trap', which Magnus suggested. It is just a reference, but it reduces the gcc compile time from 40 seconds to around 4 seconds. 10 times faster!
Is it OK to add such qemu specific options to linux kernel mainline?

Sure, why not. Try this:

---

commit eeee7853c4ffaf5b9eb58f39708e3c78f66cee15

Author: Paul Mundt <[email protected]>
Date:   Thu Apr 2 12:31:16 2009 +0900

sh: Add a command line option for disabling I/O trapping.

This adds a 'noiotrap' kernel command line option to permit disabling of I/O trapping. This is mostly useful for running on emulators where the physical device limitations are not an issue.

Signed-off-by Paul Mundt <[email protected]>

Documentation/kernel-parameters.txt +2 -0

index 240257d..8b2067c 100644
@@ -1544,6 +1544,8 @@ and is between 256 and 4096 characters. It is defined in the file
 			Valid arguments: on, off
 			Default: on
 
+	noiotrap	[SH] Disables trapped I/O port accesses.
+
 	noirqdebug	[X86-32] Disables the code which attempts to detect and
 			disable unhandled interrupt sources.

arch/sh/kernel/io_trapped.c +13 -0

index 39cd7f3..c22853b 100644
@@ -14,6 +14,7 @@
 #include <linux/bitops.h>
 #include <linux/vmalloc.h>
 #include <linux/module.h>
+#include <linux/init.h>
 #include <asm/system.h>
 #include <asm/mmu_context.h>
 #include <asm/uaccess.h>

@@ -32,6 +33,15 @@ EXPORT_SYMBOL_GPL(trapped_mem);
 #endif
 static DEFINE_SPINLOCK(trapped_lock);
 
+static int trapped_io_disable __read_mostly;
+
+static int __init trapped_io_setup(char *__unused)
+{
+	trapped_io_disable = 1;
+	return 1;
+}
+__setup("noiotrap", trapped_io_setup);
+
 int register_trapped_io(struct trapped_io *tiop)
 {
 	struct resource *res;

@@ -39,6 +49,9 @@ int register_trapped_io(struct trapped_io *tiop)
 	struct page *pages[TRAPPED_PAGES_MAX];
 	int k, n;
 
+	if (unlikely(trapped_io_disable))
+		return 0;
+
 	/* structure must be page aligned */
 	if ((unsigned long)tiop & (PAGE_SIZE - 1))
 		goto bad;

Shin-ichiro KAWASAKI

author Tested-by

2009-04-02 14:36 UTC #4 lore raw

In reply to Shin-ichiro KAWASAKI

Quoted 27 lines · Paul Mundt

Quoted 26 lines · Shin-ichiro KAWASAKI
Hi, Magnus! Thank you for your explanation.
Quoted 13 lines · Magnus Damm
2009/3/31 Shin-ichiro KAWASAKI <[email protected]>:
Quoted 7 lines
I'd like to ask following questions to linux-sh experts,
- Why such io-traps are used to access CF?
- Will this io-traps are used for SH7785LCR's SD card access?
I guess these io-traps can be the reason why gcc takes so much time on qemu-sh.
The r2d hardware implements 16-bit only CF interface while driver software requires 8-bit access. To work around this issue io_trapped is used to convert 8-bit accesses to 16-bit accesses. This is quite slow.
Quoted 8 lines
For more information, please see the comment in
arch/sh/boards/mach-r2d/setup.c
To improve performance, consider adding a command line flag to the kernel that disables io_trapped. This flag can then be set on the kernel command line by the person running qemu.
Hope this helps!
It really helps!

Quoted 8 lines

Quoted 7 lines
The attached patch is a rough implementation to add a command line flag 'avoid_trap', which Magnus suggested. It is just a reference, but it reduces the gcc compile time from 40 seconds to around 4 seconds. 10 times faster!
Is it OK to add such qemu specific options to linux kernel mainline?
Sure, why not. Try this:

It works fine, and gains same performance improvement as my dirty patch. Thank you Paul for your quick clean patch!

Tested-by Shin-ichiro KAWASAKI <[email protected]>

Quoted 70 lines

---

commit eeee7853c4ffaf5b9eb58f39708e3c78f66cee15

Author: Paul Mundt <[email protected]>
Date:   Thu Apr 2 12:31:16 2009 +0900

sh: Add a command line option for disabling I/O trapping.

This adds a 'noiotrap' kernel command line option to permit disabling of I/O trapping. This is mostly useful for running on emulators where the physical device limitations are not an issue.

Signed-off-by Paul Mundt <[email protected]>

Documentation/kernel-parameters.txt +2 -0

index 240257d..8b2067c 100644
@@ -1544,6 +1544,8 @@ and is between 256 and 4096 characters. It is defined in the file
 			Valid arguments: on, off
 			Default: on
 
+	noiotrap	[SH] Disables trapped I/O port accesses.
+
 	noirqdebug	[X86-32] Disables the code which attempts to detect and
 			disable unhandled interrupt sources.

arch/sh/kernel/io_trapped.c +13 -1

index 39cd7f3..c22853b 100644
@@ -14,6 +14,7 @@
 #include <linux/bitops.h>
 #include <linux/vmalloc.h>
 #include <linux/module.h>
+#include <linux/init.h>
 #include <asm/system.h>
 #include <asm/mmu_context.h>
 #include <asm/uaccess.h>

@@ -32,6 +33,15 @@ EXPORT_SYMBOL_GPL(trapped_mem);
 #endif
 static DEFINE_SPINLOCK(trapped_lock);
 
+static int trapped_io_disable __read_mostly;
+
+static int __init trapped_io_setup(char *__unused)
+{
+	trapped_io_disable = 1;
+	return 1;
+}
+__setup("noiotrap", trapped_io_setup);
+
 int register_trapped_io(struct trapped_io *tiop)
 {
 	struct resource *res;

@@ -39,6 +49,9 @@ int register_trapped_io(struct trapped_io *tiop)
 	struct page *pages[TRAPPED_PAGES_MAX];
 	int k, n;
 
+	if (unlikely(trapped_io_disable))
+		return 0;
+
 	/* structure must be page aligned */
 	if ((unsigned long)tiop & (PAGE_SIZE - 1))
 		goto bad;
--

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