From 6532c7fdb2c3a2ec1b949ecd2ff5375069c1639a Mon Sep 17 00:00:00 2001 From: Per Forlin Date: Fri, 19 Aug 2011 21:21:27 +0200 Subject: 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 Acked-by: Michal Nazarewicz Acked-by: Alan Stern Signed-off-by: Felipe Balbi --- drivers/usb/gadget/storage_common.c | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-) (limited to 'drivers/usb/gadget/storage_common.c') diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c index 3ea70d8549ef..9fd379998608 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 #include @@ -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) -- cgit