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 --- 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. v5: - Separate allocation of buffhds in f_mass_storage.c - Change FSG_NUM_BUFFERS to fsg_num_buffers to indicate variable value. - code clean up and document module param, all thanks to Michal and Alan. v6: - add missing kfree for buffhds and remove some redundant code.

drivers/usb/gadget/Kconfig | 16 ++++++++++++++++ drivers/usb/gadget/f_mass_storage.c | 29 +++++++++++++++++++++-------- drivers/usb/gadget/file_storage.c | 27 +++++++++++++++++---------- drivers/usb/gadget/storage_common.c | 33 +++++++++++++++++++++++++++++++-- 4 files changed, 85 insertions(+), 20 deletions(-)

diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig index 44b6b40..15e1426 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_GADGET_DEBUG_FILES 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..d2e5ee9 100644 --- a/drivers/usb/gadget/f_mass_storage.c +++ b/drivers/usb/gadget/f_mass_storage.c @@ -363,7 +363,7 @@ struct fsg_common {

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

int cmnd_size; u8 cmnd[MAX_COMMAND_SIZE]; @@ -2348,7 +2348,7 @@ reset: if (common->fsg) { fsg = common->fsg;

- for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { struct fsg_buffhd *bh = &common->buffhds[i];

if (bh->inreq) { @@ -2406,7 +2406,7 @@ reset: clear_bit(IGNORE_BULK_OUT, &fsg->atomic_bitflags);

/* Allocate the requests */ - for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { struct fsg_buffhd *bh = &common->buffhds[i];

rc = alloc_request(common, fsg->bulk_in, &bh->inreq); @@ -2475,7 +2475,7 @@ static void handle_exception(struct fsg_common *common)

/* Cancel all the pending transfers */ if (likely(common->fsg)) { - for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { bh = &common->buffhds[i]; if (bh->inreq_busy) usb_ep_dequeue(common->fsg->bulk_in, bh->inreq); @@ -2487,7 +2487,7 @@ static void handle_exception(struct fsg_common *common) /* Wait until everything is idle */ for (;;) { int num_active = 0; - for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { bh = &common->buffhds[i]; num_active += bh->inreq_busy + bh->outreq_busy; } @@ -2510,7 +2510,7 @@ static void handle_exception(struct fsg_common *common) */ spin_lock_irq(&common->lock);

- for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { bh = &common->buffhds[i]; bh->state = BUF_STATE_EMPTY; } @@ -2719,6 +2719,10 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common, int nluns, i, rc; char *pathbuf;

+ rc = fsg_num_buffers_validate(); + if (rc != 0) + return ERR_PTR(rc); + /* Find out how many LUNs there should be */ nluns = cfg->nluns; if (nluns < 1 || nluns > FSG_MAX_LUNS) { @@ -2737,6 +2741,14 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common, common->free_storage_on_release = 0; }

+ common->buffhds = kcalloc(fsg_num_buffers, + sizeof *(common->buffhds), GFP_KERNEL); + if (!common->buffhds) { + if (common->free_storage_on_release) + kfree(common); + return ERR_PTR(-ENOMEM); + } + common->ops = cfg->ops; common->private_data = cfg->private_data;

@@ -2814,7 +2826,7 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common,

/* Data buffers cyclic list */ bh = common->buffhds; - i = FSG_NUM_BUFFERS; + i = fsg_num_buffers; goto buffhds_first_it; do { bh->next = bh + 1; @@ -2940,12 +2952,13 @@ static void fsg_common_release(struct kref *ref)

{ struct fsg_buffhd *bh = common->buffhds; - unsigned i = FSG_NUM_BUFFERS; + unsigned i = fsg_num_buffers; do { kfree(bh->buf); } while (++bh, --i); }

+ kfree(common->buffhds); if (common->free_storage_on_release) kfree(common); } diff --git a/drivers/usb/gadget/file_storage.c b/drivers/usb/gadget/file_storage.c index 639e14a..ba95ef4 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[]; };

typedef void (*fsg_routine_t)(struct fsg_dev *); @@ -2752,7 +2753,7 @@ static int do_set_interface(struct fsg_dev *fsg, int altsetting)

reset: /* Deallocate the requests */ - for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { struct fsg_buffhd *bh = &fsg->buffhds[i];

if (bh->inreq) { @@ -2813,7 +2814,7 @@ reset: }

/* Allocate the requests */ - for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { struct fsg_buffhd *bh = &fsg->buffhds[i];

if ((rc = alloc_request(fsg, fsg->bulk_in, &bh->inreq)) != 0) @@ -2909,7 +2910,7 @@ static void handle_exception(struct fsg_dev *fsg) /* Cancel all the pending transfers */ if (fsg->intreq_busy) usb_ep_dequeue(fsg->intr_in, fsg->intreq); - for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { bh = &fsg->buffhds[i]; if (bh->inreq_busy) usb_ep_dequeue(fsg->bulk_in, bh->inreq); @@ -2920,7 +2921,7 @@ static void handle_exception(struct fsg_dev *fsg) /* Wait until everything is idle */ for (;;) { num_active = fsg->intreq_busy; - for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { bh = &fsg->buffhds[i]; num_active += bh->inreq_busy + bh->outreq_busy; } @@ -2942,7 +2943,7 @@ static void handle_exception(struct fsg_dev *fsg) * state, and the exception. Then invoke the handler. */ spin_lock_irq(&fsg->lock);

- for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { bh = &fsg->buffhds[i]; bh->state = BUF_STATE_EMPTY; } @@ -3172,7 +3173,7 @@ static void /* __init_or_exit */ fsg_unbind(struct usb_gadget *gadget) }

/* Free the data buffers */ - for (i = 0; i < FSG_NUM_BUFFERS; ++i) + for (i = 0; i < fsg_num_buffers; ++i) kfree(fsg->buffhds[i].buf);

/* Free the request and buffer for endpoint 0 */ @@ -3460,7 +3461,7 @@ static int __init fsg_bind(struct usb_gadget *gadget) req->complete = ep0_complete;

/* Allocate the data buffers */ - for (i = 0; i < FSG_NUM_BUFFERS; ++i) { + for (i = 0; i < fsg_num_buffers; ++i) { struct fsg_buffhd *bh = &fsg->buffhds[i];

/* Allocate for the bulk-in endpoint. We assume that @@ -3471,7 +3472,7 @@ static int __init fsg_bind(struct usb_gadget *gadget) goto out; bh->next = bh + 1; } - fsg->buffhds[FSG_NUM_BUFFERS - 1].next = &fsg->buffhds[0]; + fsg->buffhds[fsg_num_buffers - 1].next = &fsg->buffhds[0];

/* This should reflect the actual gadget power source */ usb_gadget_set_selfpowered(gadget); @@ -3587,7 +3588,9 @@ static int __init fsg_alloc(void) { struct fsg_dev *fsg;

- fsg = kzalloc(sizeof *fsg, GFP_KERNEL); + fsg = kzalloc(sizeof *fsg + + fsg_num_buffers * sizeof *(fsg->buffhds), GFP_KERNEL); + if (!fsg) return -ENOMEM; spin_lock_init(&fsg->lock); @@ -3605,6 +3608,10 @@ static int __init fsg_init(void) int rc; struct fsg_dev *fsg;

+ rc = fsg_num_buffers_validate(); + if (rc != 0) + return rc; + if ((rc = fsg_alloc()) != 0) return rc; fsg = the_fsg; diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c index d3dd227..fda15fa 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> @@ -262,8 +268,31 @@ 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)