Matwey V. Kornilov 1161db6776 media: usb: pwc: Don't use coherent DMA buffers for ISO transfer ... DMA cocherency slows the transfer down on systems without hardware coherent DMA. Instead we use noncocherent DMA memory and explicit sync at data receive handler. Based on previous commit the following performance benchmarks have been carried out. Average memcpy() data transfer rate (rate) and handler completion time (time) have been measured when running video stream at 640x480 resolution at 10fps. x86_64 based system (Intel Core i5-3470). This platform has hardware coherent DMA support and proposed change doesn't make big difference here. * kmalloc: rate = (2.0 +- 0.4) GBps time = (5.0 +- 3.0) usec * usb_alloc_coherent: rate = (3.4 +- 1.2) GBps time = (3.5 +- 3.0) usec We see that the measurements agree within error ranges in this case. So theoretically predicted performance downgrade cannot be reliably measured here. armv7l based system (TI AM335x BeagleBone Black @ 300MHz). This platform has no hardware coherent DMA support. DMA coherence is implemented via disabled page caching that slows down memcpy() due to memory controller behaviour. * kmalloc: rate = ( 94 +- 4) MBps time = (101 +- 4) usec * usb_alloc_coherent: rate = (28.1 +- 0.1) MBps time = (341 +- 2) usec Note, that quantative difference leads (this commit leads to 3.3 times acceleration) to qualitative behavior change in this case. As it was stated before, the video stream cannot be successfully received at AM335x platforms with MUSB based USB host controller due to performance issues [1]. [1] https://www.spinics.net/lists/linux-usb/msg165735.html Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>		2019-01-16 11:16:06 -05:00
..
Kconfig
Makefile
pwc-ctrl.c	Replace <asm/uaccess.h> with <linux/uaccess.h> globally	2016-12-24 11:46:01 -08:00
pwc-dec1.c
pwc-dec1.h
pwc-dec23.c	media: drivers: remove "/**" from non-kernel-doc comments	2017-11-30 04:19:03 -05:00
pwc-dec23.h
pwc-if.c	media: usb: pwc: Don't use coherent DMA buffers for ISO transfer	2019-01-16 11:16:06 -05:00
pwc-kiara.c
pwc-kiara.h
pwc-misc.c
pwc-nala.h	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
pwc-timon.c
pwc-timon.h
pwc-uncompress.c	[media] media: videobuf2: Restructure vb2_buffer	2015-10-01 09:04:43 -03:00
pwc-v4l.c	media: replace strcpy() by strscpy()	2018-09-11 13:32:17 -04:00
pwc.h	media: replace all <spaces><tab> occurrences	2018-01-04 13:15:05 -05:00