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author | Per Forlin <per.forlin@linaro.org> | 2011-08-19 21:21:27 +0200 |
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committer | Felipe Balbi <balbi@ti.com> | 2011-09-09 13:06:04 +0300 |
commit | 6532c7fdb2c3a2ec1b949ecd2ff5375069c1639a (patch) | |
tree | 26afd8fdff7923f818f49aa405bb4208d1da914e /drivers/usb/gadget/storage_common.c | |
parent | 04eee25b1d754a837360504b7af426d1f86ffeb7 (diff) | |
download | op-kernel-dev-6532c7fdb2c3a2ec1b949ecd2ff5375069c1639a.zip op-kernel-dev-6532c7fdb2c3a2ec1b949ecd2ff5375069c1639a.tar.gz |
usb: gadget: storage: make FSG_NUM_BUFFERS variable size
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_governor 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_GADGET_DEBUG_FILES
this value may be set by a module parameter as well.
Signed-off-by: Per Forlin <per.forlin@linaro.org>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Diffstat (limited to 'drivers/usb/gadget/storage_common.c')
-rw-r--r-- | drivers/usb/gadget/storage_common.c | 33 |
1 files changed, 31 insertions, 2 deletions
diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c index 3ea70d8..9fd3799 100644 --- a/drivers/usb/gadget/storage_common.c +++ b/drivers/usb/gadget/storage_common.c @@ -52,6 +52,12 @@ * characters rather then a pointer to void. */ +/* + * When USB_GADGET_DEBUG_FILES is defined the module param num_buffers + * sets the number of pipeline buffers (length of the fsg_buffhd array). + * The valid range of num_buffers is: num >= 2 && num <= 4. + */ + #include <linux/usb/storage.h> #include <scsi/scsi.h> @@ -264,8 +270,31 @@ 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_GADGET_DEBUG_FILES + +static unsigned int fsg_num_buffers = CONFIG_USB_GADGET_STORAGE_NUM_BUFFERS; +module_param_named(num_buffers, fsg_num_buffers, uint, S_IRUGO); +MODULE_PARM_DESC(num_buffers, "Number of pipeline 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 */ + +/* check if fsg_num_buffers is within a valid range */ +static inline int fsg_num_buffers_validate(void) +{ + if (fsg_num_buffers >= 2 && fsg_num_buffers <= 4) + return 0; + pr_err("fsg_num_buffers %u is out of range (%d to %d)\n", + fsg_num_buffers, 2 ,4); + return -EINVAL; +} /* Default size of buffer length. */ #define FSG_BUFLEN ((u32)16384) |