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Subject[PATCH v4] usb: gadget: storage_common: make FSG_NUM_BUFFERS variable size
Date
From: Per Forlin <per.forlin@linaro.org>

FSG_NUM_BUFFERS is set to 2 as default.
Usually 2 buffers are enough to establish a good buffering pipeline.
The number may be increased in order to compensate a for bursty VFS
behaviour.

Here follows a description of system that may require more than
2 buffers.
* CPU ondemand governor active
* latency cost for wake up and/or frequency change
* DMA for IO

Use case description.
* Data transfer from MMC via VFS to USB.
* DMA shuffles data from MMC and to USB.
* The CPU wakes up every now and then to pass data in and out from VFS,
which cause the bursty VFS behaviour.

Test set up
* Running dd on the host reading from the mass storage device
* cmdline: dd if=/dev/sdb of=/dev/null bs=4k count=$((256*100))
* Caches are dropped on the host and on the device before each run

Measurements on a Snowball board with ondemand_govenor active.

FSG_NUM_BUFFERS 2
104857600 bytes (105 MB) copied, 5.62173 s, 18.7 MB/s
104857600 bytes (105 MB) copied, 5.61811 s, 18.7 MB/s
104857600 bytes (105 MB) copied, 5.57817 s, 18.8 MB/s

FSG_NUM_BUFFERS 4
104857600 bytes (105 MB) copied, 5.26839 s, 19.9 MB/s
104857600 bytes (105 MB) copied, 5.2691 s, 19.9 MB/s
104857600 bytes (105 MB) copied, 5.2711 s, 19.9 MB/s

There may not be one optimal number for all boards. This is why
the number is added to Kconfig. If selecting USB_DEBUG this value may be
set by a module parameter as well.

Signed-off-by: Per Forlin <per.forlin@linaro.org>
---
Change log.
v2: Update after proofreading comments from Michal Nazarewicz
v3: Clarify the description of this patch based on input from Alan Stern
v4: - Introduce a module_param to set number of pipeline buffers
if USB_DEBUG is set. In order to add this support fsg_common is
allocated at runtime. The fsg_buffhd list size is appended to fsg_dev
and fsg_common at runtime allocation.
- The previous acks from Michal and Alan on v3 are not applicable
for this version since it's a new implementation.
drivers/usb/gadget/Kconfig | 16 ++++++++++++++++
drivers/usb/gadget/f_mass_storage.c | 10 +++++++---
drivers/usb/gadget/file_storage.c | 10 ++++++++--
drivers/usb/gadget/mass_storage.c | 16 +++++++++-------
drivers/usb/gadget/storage_common.c | 20 ++++++++++++++++++--
5 files changed, 58 insertions(+), 14 deletions(-)
diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
index 44b6b40..37ec2ce 100644
--- a/drivers/usb/gadget/Kconfig
+++ b/drivers/usb/gadget/Kconfig
@@ -96,6 +96,22 @@ config USB_GADGET_VBUS_DRAW
This value will be used except for system-specific gadget
drivers that have more specific information.

+config USB_GADGET_STORAGE_NUM_BUFFERS
+ int "Number of storage pipeline buffers"
+ range 2 4
+ default 2
+ help
+ Usually 2 buffers are enough to establish a good buffering
+ pipeline. The number may be increased in order to compensate
+ for a bursty VFS behaviour. For instance there may be cpu wake up
+ latencies that makes the VFS to appear bursty in a system with
+ an cpu on-demand governor. Especially if DMA is doing IO to
+ offload the CPU. In this case the CPU will go into power
+ save often and spin up occasionally to move data within VFS.
+ If selecting USB_DEBUG this value may be set by a module
+ parameter as well.
+ If unsure, say 2.
+
#
# USB Peripheral Controller Support
#
diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index 5b93395..3e546d9 100644
--- a/drivers/usb/gadget/f_mass_storage.c
+++ b/drivers/usb/gadget/f_mass_storage.c
@@ -363,7 +363,6 @@ struct fsg_common {

struct fsg_buffhd *next_buffhd_to_fill;
struct fsg_buffhd *next_buffhd_to_drain;
- struct fsg_buffhd buffhds[FSG_NUM_BUFFERS];

int cmnd_size;
u8 cmnd[MAX_COMMAND_SIZE];
@@ -407,6 +406,8 @@ struct fsg_common {
char inquiry_string[8 + 16 + 4 + 1];

struct kref ref;
+ /* Must be the last entry */
+ struct fsg_buffhd buffhds[0];
};

struct fsg_config {
@@ -2728,12 +2729,15 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common,

/* Allocate? */
if (!common) {
- common = kzalloc(sizeof *common, GFP_KERNEL);
+ common = kzalloc(sizeof(struct fsg_common) +
+ sizeof(struct fsg_buffhd) * FSG_NUM_BUFFERS,
+ GFP_KERNEL);
if (!common)
return ERR_PTR(-ENOMEM);
common->free_storage_on_release = 1;
} else {
- memset(common, 0, sizeof *common);
+ memset(common, 0, sizeof(struct fsg_common) +
+ sizeof(struct fsg_buffhd) * FSG_NUM_BUFFERS);
common->free_storage_on_release = 0;
}

diff --git a/drivers/usb/gadget/file_storage.c b/drivers/usb/gadget/file_storage.c
index 639e14a..21d366d 100644
--- a/drivers/usb/gadget/file_storage.c
+++ b/drivers/usb/gadget/file_storage.c
@@ -461,7 +461,6 @@ struct fsg_dev {

struct fsg_buffhd *next_buffhd_to_fill;
struct fsg_buffhd *next_buffhd_to_drain;
- struct fsg_buffhd buffhds[FSG_NUM_BUFFERS];

int thread_wakeup_needed;
struct completion thread_notifier;
@@ -488,6 +487,8 @@ struct fsg_dev {
unsigned int nluns;
struct fsg_lun *luns;
struct fsg_lun *curlun;
+ /* Must be the last entry */
+ struct fsg_buffhd buffhds[0];
};

typedef void (*fsg_routine_t)(struct fsg_dev *);
@@ -3587,7 +3588,9 @@ static int __init fsg_alloc(void)
{
struct fsg_dev *fsg;

- fsg = kzalloc(sizeof *fsg, GFP_KERNEL);
+ fsg = kzalloc(sizeof(struct fsg_dev) +
+ sizeof(struct fsg_buffhd) * FSG_NUM_BUFFERS, GFP_KERNEL);
+
if (!fsg)
return -ENOMEM;
spin_lock_init(&fsg->lock);
@@ -3605,6 +3608,9 @@ static int __init fsg_init(void)
int rc;
struct fsg_dev *fsg;

+ if (!FSG_NUM_BUFFERS_IS_VALID(FSG_NUM_BUFFERS))
+ return -EINVAL;
+
if ((rc = fsg_alloc()) != 0)
return rc;
fsg = the_fsg;
diff --git a/drivers/usb/gadget/mass_storage.c b/drivers/usb/gadget/mass_storage.c
index d3eb274..67c58d0 100644
--- a/drivers/usb/gadget/mass_storage.c
+++ b/drivers/usb/gadget/mass_storage.c
@@ -116,9 +116,8 @@ static int __init msg_do_config(struct usb_configuration *c)
static const struct fsg_operations ops = {
.thread_exits = msg_thread_exits,
};
- static struct fsg_common common;
+ struct fsg_common *common = NULL;

- struct fsg_common *retp;
struct fsg_config config;
int ret;

@@ -130,12 +129,12 @@ static int __init msg_do_config(struct usb_configuration *c)
fsg_config_from_params(&config, &mod_data);
config.ops = &ops;

- retp = fsg_common_init(&common, c->cdev, &config);
- if (IS_ERR(retp))
- return PTR_ERR(retp);
+ common = fsg_common_init(common, c->cdev, &config);
+ if (IS_ERR(common))
+ return PTR_ERR(common);

- ret = fsg_bind_config(c->cdev, c, &common);
- fsg_common_put(&common);
+ ret = fsg_bind_config(c->cdev, c, common);
+ fsg_common_put(common);
return ret;
}

@@ -179,6 +178,9 @@ MODULE_LICENSE("GPL");

static int __init msg_init(void)
{
+ if (!FSG_NUM_BUFFERS_IS_VALID(FSG_NUM_BUFFERS))
+ return -EINVAL;
+
return usb_composite_probe(&msg_driver, msg_bind);
}
module_init(msg_init);
diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c
index d3dd227..197eace 100644
--- a/drivers/usb/gadget/storage_common.c
+++ b/drivers/usb/gadget/storage_common.c
@@ -262,8 +262,24 @@ static struct fsg_lun *fsg_lun_from_dev(struct device *dev)
#define EP0_BUFSIZE 256
#define DELAYED_STATUS (EP0_BUFSIZE + 999) /* An impossibly large value */

-/* Number of buffers we will use. 2 is enough for double-buffering */
-#define FSG_NUM_BUFFERS 2
+#ifdef CONFIG_USB_DEBUG
+
+static unsigned int fsg_num_buffers = CONFIG_USB_GADGET_STORAGE_NUM_BUFFERS;
+module_param(fsg_num_buffers, uint, S_IRUGO);
+MODULE_PARM_DESC(fsg_num_buffers, "Number of pipeline buffers");
+#define FSG_NUM_BUFFERS fsg_num_buffers
+
+#else
+
+/*
+ * Number of buffers we will use.
+ * 2 is usually enough for good buffering pipeline
+ */
+#define FSG_NUM_BUFFERS CONFIG_USB_GADGET_STORAGE_NUM_BUFFERS
+
+#endif /* CONFIG_USB_DEBUG */
+
+#define FSG_NUM_BUFFERS_IS_VALID(num) (num >= 2 && num <= 4 ? true : false)

/* Default size of buffer length. */
#define FSG_BUFLEN ((u32)16384)
--
1.7.4.1


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