On 19 August 2011 16:28, Per Forlin per.forlin@stericsson.com wrote:
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_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.
drivers/usb/gadget/Kconfig | 16 ++++++++++++++++ drivers/usb/gadget/f_mass_storage.c | 24 ++++++++++++++++-------- drivers/usb/gadget/file_storage.c | 26 ++++++++++++++++---------- drivers/usb/gadget/mass_storage.c | 3 +++ drivers/usb/gadget/multi.c | 3 +++ drivers/usb/gadget/storage_common.c | 25 +++++++++++++++++++++++-- 6 files changed, 77 insertions(+), 20 deletions(-)
diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig index 44b6b40..65ceecf 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..49da6a1 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; } @@ -2737,6 +2737,14 @@ 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);
Need to add a kfree() at release too. This data is never freed otherwise. I'll update fix that in the next version together with any new comments from Michal and Alan.
/Per