Messages in this thread Patch in this message | | | Subject | Re: [PATCH] usb: gadget: storage_common: make FSG_NUM_BUFFERS variable size | Date | Mon, 08 Aug 2011 11:40:09 +0200 | From | "Michal Nazarewicz" <> |
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On Mon, 08 Aug 2011 02:22:14 +0200, Per Forlin <per.forlin@linaro.org> 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, so adding Kconfig should be enough for now.
> Signed-off-by: Per Forlin <per.forlin@linaro.org>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Some not very relevant comments below:
> 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”.
> + 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”.
> + 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.
> + 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.
> + 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/?
> +#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@google.com>-----ooO--(_)--Ooo-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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