Hi Michal, 2011/8/8 Michal Nazarewicz <mina86@xxxxxxxxxx>: > On Mon, 08 Aug 2011 02:22:14 +0200, Per Forlin <per.forlin@xxxxxxxxxx> > wrote: >> >> FSG_NUM_BUFFERS is set to 2 as default. >> Usually 2 buffers are enough to establish a good >> double buffering pipeline. But when dealing with expensive >> request preparation (i.e. dma_map) there may be benefits of >> increasing the number of buffers. There is an extra cost for >> every first request, the others are prepared in parallell with >> an ongoing transfer. Every time all buffers are consumed there is >> an additional cost for the next first request. Increasing the number >> of buffers decreases the risk of running out of buffers. > > [... benchmark snip ...] > >> There may not be one optimal number for all boards. That is the >> reason for adding the number to Kconfig, > > It could actually be turned into a run-time configuration, but > that's a bit more intrusive, I consider this too but couldn't see how this would be done nicely. >> Signed-off-by: Per Forlin <per.forlin@xxxxxxxxxx> > > Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx> > > > Some not very relevant comments below: Thanks for these pointers. I'll update. > >> diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig >> index 029e288..bbd17f3 100644 >> --- a/drivers/usb/gadget/Kconfig >> +++ b/drivers/usb/gadget/Kconfig >> @@ -96,6 +96,21 @@ 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 pipline buffers" > > “pipeline”, missing “e”. Will fix. > >> + range 2 64 >> + default 2 >> + help >> + Usually 2 buffers are enough to establish a good >> + double buffering pipeline. But when dealing with expensive > > s/double//. By definition, “double” buffering uses two buffers, isn't it? > So if we change number of buffers, it's no longer “double”. > Good point! >> + request preparation (i.e. dma_map) there may be benefits of >> + increasing the number of buffers. There is an extra cost for >> + every first request, the others are prepared in parallell with > > “parallel”, too many “l”s. > Will fix >> + an ongoing transfer. Every time all buffers are consumed there >> is >> + an additional cost for the next first request. Increasing the >> number > > “Next first request” sounds a bit illogical to me. > I'll remove "next" to avoid confusion. >> + of buffers decreases the risk of running out of buffers. >> + If unsure, say 2. >> + >> config USB_GADGET_SELECTED >> boolean >> diff --git a/drivers/usb/gadget/storage_common.c >> b/drivers/usb/gadget/storage_common.c >> index 1fa4f70..512d9cf 100644 >> --- a/drivers/usb/gadget/storage_common.c >> +++ b/drivers/usb/gadget/storage_common.c >> @@ -262,8 +262,8 @@ 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 >> +/* Number of buffers we will use. 2 is usually enough for >> double-buffering */ > > s/double-buffering/good buffering pipeline/? > Will fix. >> +#define FSG_NUM_BUFFERS CONFIG_USB_GADGET_STORAGE_NUM_BUFFERS >> /* Default size of buffer length. */ >> #define FSG_BUFLEN ((u32)16384) > > -- > Best regards, _ _ > .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o > ..o | Computer Science, Michal "mina86" Nazarewicz (o o) > ooo +-----<email/xmpp: mnazarewicz@xxxxxxxxxx>-----ooO--(_)--Ooo-- > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
