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cd38557d78
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Ben Hutchings cd38557d78 sfc: Use TX push whenever adding descriptors to an empty queue 
Whenever we add DMA descriptors to a TX ring and update the ring
pointer, the TX DMA engine must first read the new DMA descriptors and
then start reading packet data.  However, all released Solarflare 10G
controllers have a 'TX push' feature that allows us to reduce latency
by writing the first new DMA descriptor along with the pointer update.
This is only useful when the queue is empty.  The hardware should
ignore the pushed descriptor if the queue is not empty, but this check
is buggy, so we must do it in software.

In order to tell whether a TX queue is empty, we need to compare the
previous transmission count (write_count) and completion count
(read_count).  However, if we do that every time we update the ring
pointer then read_count may ping-pong between the caches of two CPUs
running the transmission and completion paths for the queue.
Therefore, we split the check for an empty queue between the
completion path and the transmission path:

- Add an empty_read_count field representing a point at which the
  completion path saw the TX queue as empty.
- Add an old_write_count field for use on the completion path.
- On the completion path, whenever read_count reaches or passes
  old_write_count the TX queue may be empty.  We then read
  write_count, set empty_read_count if read_count == write_count,
  and update old_write_count.
- On the transmission path, we read empty_read_count.  If it's set, we
  compare it with the value of write_count before the current set of
  descriptors was added.  If they match, the queue really is empty and
  we can use TX push.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
2010-12-06 23:00:07 +00:00
..
accessibility
acpi Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6 2010-10-26 17:28:37 -07:00
amba
ata drivers/ata/pata_octeon_cf.c: delete double assignment 2010-11-12 17:10:55 -05:00
atm atm: fore200e: Fix build warning. 2010-11-18 11:49:25 -08:00
auxdisplay
base Merge branch 'pm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/suspend-2.6 2010-10-29 15:09:56 -07:00
block Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6 2010-11-14 11:57:05 -08:00
bluetooth Bluetooth: Add MacBookAir3,1(2) support 2010-11-09 01:08:53 -02:00
cdrom cdrom: gdrom: ctrl_in/outX to __raw_read/writeX conversion. 2010-10-27 14:33:39 +09:00
char Merge branch 'tty-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty-2.6 2010-11-12 16:02:30 -08:00
clocksource ARM: shmobile: remove sh_timer_config clk member 2010-10-31 10:40:39 -04:00
connector connector: remove lazy workqueue creation 2010-10-24 14:20:01 -07:00
cpufreq [CPUFREQ] add sampling_down_factor tunable to improve ondemand performance 2010-10-22 11:44:47 -04:00
cpuidle
crypto replace nested max/min macros with {max,min}3 macro 2010-10-26 16:52:12 -07:00
dca
dio
dma drivers/dma/Kconfig: add part number for Topcliff. 2010-10-29 14:14:02 -07:00
edac Merge branch 'linux_next' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/i7core 2010-10-26 10:13:48 -07:00
eisa
firewire Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/ieee1394/linux1394-2.6 2010-11-05 14:17:22 -07:00
firmware dmi: log board, system, and BIOS information 2010-10-27 18:03:05 -07:00
gpio gpio: Add VIA VX855 GPIO driver 2010-10-29 00:29:51 +02:00
gpu drm/ttm: Be consistent on ttm_bo_init() failures 2010-11-10 11:52:19 +10:00
hid Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2010-10-25 07:59:01 -07:00
hwmon hwmon: (gpio-fan) Fix fan_ctrl_init error path 2010-11-11 09:43:51 -08:00
i2c i2c-i801: Add PCI idents for Patsburg 'IDF' SMBus controllers 2010-10-31 21:07:00 +01:00
ide ide: clean up timed out request handling 2010-10-26 10:17:30 -07:00
idle Merge branch 'idle-release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-idle-2.6 2010-10-26 17:28:07 -07:00
ieee802154
infiniband infiniband: remove dev_base_lock use 2010-11-24 11:41:56 -08:00
input Input: do not pass injected events back to the originating handler 2010-11-11 01:01:26 -08:00
isdn filter: optimize sk_run_filter 2010-11-19 09:49:59 -08:00
leds drivers/leds/leds-gpio.c: properly initialize return value 2010-11-12 07:55:32 -08:00
lguest
macintosh drivers/macintosh/adb-iop.c: flags should be unsigned long 2010-11-12 07:55:30 -08:00
mca
md block: read i_size with i_size_read() 2010-11-10 14:40:53 +01:00
media Input: ir-keytable - fix uninitialized variable warning 2010-10-31 21:05:43 -04:00
memstick
message Merge git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6 2010-10-22 17:34:15 -07:00
mfd mfd: Fix a memory leak when unload mc13xxx-core module 2010-10-29 00:30:43 +02:00
misc drivers/misc/bh1770glc.c: error handling in bh1770_power_state_store() 2010-11-12 07:55:31 -08:00
mmc mfd: Adding twl6030 mmc card detect support for MMC1 2010-10-29 00:29:59 +02:00
mtd Merge git://git.infradead.org/mtd-2.6 2010-10-30 08:31:35 -07:00
net sfc: Use TX push whenever adding descriptors to an empty queue 2010-12-06 23:00:07 +00:00
nubus
of of/mips: Cleanup some include directives/files. 2010-10-21 11:10:11 -06:00
oprofile Merge branches 'perf-fixes-for-linus' and 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-10-30 11:43:26 -07:00
parisc Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/kyle/parisc-2.6 2010-10-28 09:24:14 -07:00
parport Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2010-10-24 13:41:39 -07:00
pci xen-pcifront: fix PCI reference leak 2010-11-08 11:41:15 -05:00
pcmcia Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2010-10-24 13:41:39 -07:00
platform Remove duplicate includes from many files 2010-10-27 18:03:18 -07:00
pnp Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6 2010-10-26 17:28:37 -07:00
power power: Revert "power_supply: Mark twl4030_charger as broken" 2010-10-29 00:30:44 +02:00
pps
ps3
rapidio rapidio: use resource_size() 2010-11-12 07:55:30 -08:00
regulator regulator: max8998 BUCK1/2 voltage change with use of GPIOs 2010-10-29 00:30:15 +02:00
rtc sh: mach-snapgear: Kill off machtype, consolidate board def. 2010-10-29 19:06:53 +09:00
s390 qeth: l3 fix len in tso hdr 2010-11-28 18:13:18 -08:00
sbus Merge branch 'next-devicetree' of git://git.secretlab.ca/git/linux-2.6 2010-10-25 08:19:14 -07:00
scsi block: remove REQ_HARDBARRIER 2010-11-10 14:54:09 +01:00
serial Merge branch 'tty-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty-2.6 2010-11-12 16:02:30 -08:00
sfi
sh Merge branches 'sh/pio-death', 'sh/nommu', 'sh/clkfwk', 'sh/core' and 'sh/intc-extension' into sh-fixes-for-linus 2010-11-08 09:42:43 +09:00
sn
spi Merge branch 'next-spi' of git://git.secretlab.ca/git/linux-2.6 2010-11-01 07:50:43 -04:00
ssb Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-2.6 2010-11-24 16:19:24 -05:00
staging Staging: Merge 'tidspbridge-2.6.37-rc1' into staging-linus 2010-11-11 05:14:54 -08:00
tc
telephony Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
thermal
tty n_gsm: Fix length handling 2010-11-11 11:06:09 -08:00
uio Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2010-10-24 13:41:39 -07:00
usb Merge branch 'usb-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6 2010-11-12 17:13:28 -08:00
uwb UWB: Return UWB_RSV_ALLOC_NOT_FOUND rather than crashing on NULL dereference if kzalloc fails 2010-11-11 07:14:07 -08:00
vhost Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6 2010-10-23 11:47:02 -07:00
video backlight: MacBookAir3,1(3,2) mbp-nvidia-bl support 2010-11-12 07:55:33 -08:00
virtio
vlynq
w1 w1: don't allow arbitrary users to remove w1 devices 2010-10-27 18:03:17 -07:00
watchdog WATCHDOG: octeon-wdt: Use I/O clock rate for timing calculations. 2010-10-29 19:08:42 +01:00
xen Merge branch 'upstream/core' of git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen 2010-11-12 16:01:55 -08:00
zorro zorro: Fix device_register() error handling 2010-10-22 09:43:25 +02:00
Kconfig
Makefile TTY: create drivers/tty and move the tty core files there 2010-11-05 08:10:33 -07:00