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Mikulas Patocka 8d35d3e37e dm kcopyd: delay unplugging 
Make kcopyd merge more I/O requests by using device unplugging.

Without this patch, each I/O request is dispatched separately to the device.
If the device supports tagged queuing, there are many small requests sent
to the device. To improve performance, this patch will batch as many requests
as possible, allowing the queue to merge consecutive requests, and send them
to the device at once.

In my tests (15k SCSI disk), this patch improves sequential write throughput:

  Sequential write throughput (chunksize of 4k, 32k, 512k)
  unpatched: 15.2, 18.5, 17.5 MB/s
  patched:   14.4, 22.6, 23.0 MB/s

In most common uses (snapshot or two-way mirror), kcopyd is only used for
two devices, one for reading and the other for writing, thus this optimization
is implemented only for two devices. The optimization may be extended to n-way
mirrors with some code complexity increase.

We keep track of two block devices to unplug (one for read and the
other for write) and unplug them when exiting "do_work" thread.  If
there are more devices used (in theory it could happen, in practice it
is rare), we unplug immediately.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-01-13 19:59:50 +00:00
..
accessibility
acpi Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
amba
ata Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
atm Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
auxdisplay
base Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
block Merge branch 'for-2.6.38/drivers' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:50:24 -08:00
bluetooth
cdrom Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
char Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
clk
clocksource
connector
cpufreq perf: Clean up power events by introducing new, more generic ones 2011-01-04 08:16:54 +01:00
cpuidle Merge branch 'for-2.6.38' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu 2011-01-07 17:02:58 -08:00
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2011-01-13 10:25:58 -08:00
dca dca: remove unneeded NULL check 2011-01-13 08:03:09 -08:00
dio
dma Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
edac Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
eisa
firewire firewire: ohci: fix compilation on arches without PAGE_KERNEL_RO 2011-01-13 15:48:29 +01:00
firmware
gpio Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6 2011-01-13 10:32:54 -08:00
gpu Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
hid Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid 2011-01-13 09:58:38 -08:00
hwmon hwmon: (dme1737) Minor cleanups 2011-01-12 21:55:13 +01:00
i2c Merge branch 'for-linus/i2c-2638' of git://git.fluff.org/bjdooks/linux 2011-01-13 10:40:57 -08:00
ide
idle perf: Clean up power events by introducing new, more generic ones 2011-01-04 08:16:54 +01:00
ieee802154
infiniband Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
input Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
isdn Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
leds leds: add output inversion option to backlight trigger 2011-01-13 08:03:06 -08:00
lguest
macintosh Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
mca
md dm kcopyd: delay unplugging 2011-01-13 19:59:50 +00:00
media Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
memstick memstick: factor out transfer initiating functionality in mspro_block.c 2011-01-13 08:03:22 -08:00
message Merge branch 'master' into for-next 2010-12-22 18:57:02 +01:00
mfd Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6 2011-01-13 10:32:54 -08:00
misc Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
mmc Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
mtd Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
net Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
nfc NFC: Driver for NXP Semiconductors PN544 NFC chip. 2011-01-13 08:03:19 -08:00
nubus
of Merge remote branch 'gcl/next' into next 2011-01-11 15:10:08 +11:00
oprofile
parisc
parport
pci Merge branch 'stable/xenbus' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen 2011-01-12 08:37:35 -08:00
pcmcia Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
platform Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
pnp
power Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
pps pps: add parallel port PPS signal generator 2011-01-13 08:03:21 -08:00
ps3
rapidio rapidio: add new idt sRIO switches 2011-01-13 08:03:18 -08:00
regulator Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6 2011-01-13 10:32:54 -08:00
rtc rtc: rtc-max6902 - set driver data in max6902_probe() 2011-01-13 08:03:12 -08:00
s390 Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
sbus sparc: explicitly cast negative phandle checks to s32 2011-01-03 20:02:06 -07:00
scsi Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
serial serial: sh-sci: build fixes. 2011-01-13 15:46:35 +09:00
sfi
sh headers: kobject.h redux 2011-01-10 08:51:44 -08:00
sn
spi Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
ssb ssb: Use pci_is_pcie() 2010-12-22 15:43:26 -05:00
staging Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6 2011-01-13 10:27:28 -08:00
tc
telephony Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
thermal
tty Merge branch 'tty-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty-2.6 2011-01-07 14:39:20 -08:00
uio
usb Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block 2011-01-13 10:45:01 -08:00
uwb
vhost
video Merge git://git.kernel.org/pub/scm/linux/kernel/git/lethal/fbdev-2.6 2011-01-13 10:39:14 -08:00
virtio
vlynq
w1 w1: DS2423 counter driver and documentation 2011-01-13 08:03:22 -08:00
watchdog watchdog: Add MCF548x watchdog driver. 2011-01-12 13:51:35 +00:00
xen Merge branch 'stable/xenbus' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen 2011-01-12 08:37:35 -08:00
zorro
Kconfig NFC: Driver for NXP Semiconductors PN544 NFC chip. 2011-01-13 08:03:19 -08:00
Makefile NFC: Driver for NXP Semiconductors PN544 NFC chip. 2011-01-13 08:03:19 -08:00