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Shaohua Li 12cee5a8a2 md/raid1: prevent merging too large request 
For SSD, if request size exceeds specific value (optimal io size), request size
isn't important for bandwidth. In such condition, if making request size bigger
will cause some disks idle, the total throughput will actually drop. A good
example is doing a readahead in a two-disk raid1 setup.

So when should we split big requests? We absolutly don't want to split big
request to very small requests. Even in SSD, big request transfer is more
efficient. This patch only considers request with size above optimal io size.

If all disks are busy, is it worth doing a split? Say optimal io size is 16k,
two requests 32k and two disks. We can let each disk run one 32k request, or
split the requests to 4 16k requests and each disk runs two. It's hard to say
which case is better, depending on hardware.

So only consider case where there are idle disks. For readahead, split is
always better in this case. And in my test, below patch can improve > 30%
thoughput. Hmm, not 100%, because disk isn't 100% busy.

Such case can happen not just in readahead, for example, in directio. But I
suppose directio usually will have bigger IO depth and make all disks busy, so
I ignored it.

Note: if the raid uses any hard disk, we don't prevent merging. That will make
performace worse.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
2012-07-31 10:03:53 +10:00
..
accessibility
acpi Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux 2012-07-14 12:44:26 -07:00
amba arm-soc: driver specific updates 2012-05-26 12:22:27 -07:00
ata Viresh has moved 2012-06-20 14:39:36 -07:00
atm solos-pci: Fix DMA support 2012-05-24 16:22:53 -04:00
auxdisplay
base PM / Sleep: Prevent waiting forever on asynchronous suspend after abort 2012-06-24 23:31:09 +02:00
bcma bcma: fix null pointer in bcma_core_pci_irq_ctl 2012-06-08 13:47:07 -04:00
block blk: fix wrong idr_pre_get() error check in loop.c 2012-07-14 15:39:58 -07:00
bluetooth Bluetooth: btmrvl: Do not send vendor events to bluetooth stack 2012-06-19 00:19:11 -03:00
cdrom
char Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2012-06-18 12:20:36 -07:00
clk clk: fix parent validation in __clk_set_parent() 2012-07-03 12:05:14 -07:00
clocksource clocksource: sh_tmu: Use clockevents_config_and_register(). 2012-06-11 17:10:16 +09:00
connector
cpufreq
cpuidle
crypto arm-soc: clock driver changes 2012-05-26 12:42:29 -07:00
dca
devfreq Power management updates for 3.5 2012-05-23 14:07:06 -07:00
dio
dma Merge branch 'fixes' of git://git.infradead.org/users/vkoul/slave-dma 2012-06-20 22:12:52 -07:00
edac edac: Do alignment logic properly in edac_align_ptr() 2012-06-11 12:43:16 -03:00
eisa
extcon extcon: max8997: Add missing kfree for info->edev in max8997_muic_remove() 2012-06-18 16:30:42 -07:00
firewire IEEE 1394 (FireWire) subsystem updates post v3.4: 2012-05-24 12:57:47 -07:00
firmware
gpio gpio/gpio-tps65910: gpio_chip.of_node referenced without CONFIG_OF_GPIO defined 2012-07-10 22:53:31 +02:00
gpu drm/i915: kick any firmware framebuffers before claiming the gtt 2012-07-03 11:18:48 +01:00
hid Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2012-07-13 10:33:18 -07:00
hsi
hv Driver core pull for 3.5-rc1 2012-05-22 16:02:13 -07:00
hwmon hwmon: (it87) Preserve configuration register bits on init 2012-07-12 22:47:37 +02:00
hwspinlock hwspinlock/core: use global ID to register hwspinlocks on multiple devices 2012-07-07 22:35:30 +03:00
i2c i2c: Add generic I2C multiplexer using pinctrl API 2012-06-04 16:49:43 +02:00
ide drivers/ide/ide-cs.c: adjust suspicious bit operation 2012-06-12 15:51:41 -07:00
idle
ieee802154
iio iio: drop wrong reference from Kconfig 2012-06-14 17:28:46 -07:00
infiniband Merge branches 'cma' and 'ocrdma' into for-linus 2012-06-24 04:59:59 -07:00
input Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2012-07-13 10:33:18 -07:00
iommu iommu/amd: fix type bug in flush code 2012-07-02 12:11:40 +02:00
isdn Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2012-05-24 11:54:29 -07:00
leds leds: heartbeat: fix bug on panic 2012-07-04 15:55:19 +08:00
lguest
macintosh
md md/raid1: prevent merging too large request 2012-07-31 10:03:53 +10:00
media Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media 2012-07-13 10:29:41 -07:00
memory
memstick
message Merge branch 'akpm' (Andrew's patch-bomb) 2012-05-31 18:10:18 -07:00
mfd mfd: Add missing hunk to change palmas irq to clear on read 2012-07-09 00:16:26 +02:00
misc Merge branch 'akpm' (Andrew's patch-bomb) 2012-07-11 16:06:54 -07:00
mmc mmc: cd-gpio: pass IRQF_ONESHOT to request_threaded_irq() 2012-07-10 23:03:57 -04:00
mtd Late MTD fixes for 3.5: 2012-07-13 09:56:26 -07:00
net e1000e: remove use of IP payload checksum 2012-07-01 00:25:32 -07:00
nfc NFC: potential integer overflow problem in check_crc() 2012-05-25 11:16:16 -04:00
nubus
of ARM: SoC fixes for 3.5-rc 2012-07-11 12:44:25 -07:00
oprofile oprofile: perf: use NR_CPUS instead or nr_cpumask_bits for static array 2012-06-21 16:15:11 +02:00
parisc Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2012-05-22 19:22:50 -07:00
parport Driver core pull for 3.5-rc1 2012-05-22 16:02:13 -07:00
pci PCI: EHCI: fix crash during suspend on ASUS computers 2012-07-10 09:52:05 -07:00
pcmcia
pinctrl Merge branch 'akpm' (Andrew's patch-bomb) 2012-06-20 14:41:57 -07:00
platform drivers/platform/x86/acerhdf.c: correct Boris' mail address 2012-06-07 14:43:55 -07:00
pnp
power A bunch of fixes for v3.5, nothing extraordinary. 2012-05-31 12:10:15 -07:00
pps
ps3
ptp Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2012-05-22 19:22:50 -07:00
rapidio rapidio/tsi721: add DMA engine support 2012-05-31 17:49:31 -07:00
regulator regulator: Fix recursive mutex lockdep warning 2012-07-03 20:25:58 +01:00
remoteproc remoteproc: fix missing CONFIG_FW_LOADER configurations 2012-07-04 11:01:12 +03:00
rpmsg rpmsg: make sure inflight messages don't invoke just-removed callbacks 2012-07-04 11:51:59 +03:00
rtc drivers/rtc/rtc-twl.c: fix threaded IRQ to use IRQF_ONESHOT 2012-07-11 16:04:48 -07:00
s390 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2012-05-31 10:51:10 -07:00
sbus
scsi [SCSI] bnx2i: Removed the reference to the netdev->base_addr 2012-07-08 09:52:03 +01:00
sfi
sh sh: intc: Kill off special reservation interface. 2012-05-22 19:07:55 +09:00
sn
spi SPI: fix over-eager devm_xxx() conversion 2012-06-18 11:27:04 +01:00
ssb
staging Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media 2012-06-25 14:53:09 -07:00
target tcm_fc: Resolve suspicious RCU usage warnings 2012-07-06 12:52:09 -07:00
tc
thermal
tty tty/hvc_opal: Fix debug function name 2012-07-10 19:16:25 +10:00
uio
usb MFD Fixes for 3.5 2012-07-13 09:54:26 -07:00
uwb
vhost vhost: use USER_DS in vhost_worker thread 2012-06-26 21:10:56 -07:00
video fbdev fixes for 3.5 2012-07-11 16:17:14 -07:00
virt
virtio virtio-balloon: fix add/get API use 2012-07-09 09:07:22 +09:30
vlynq
vme
w1 arm-soc: clock driver changes 2012-05-26 12:42:29 -07:00
watchdog watchdog: core: fix WDIOC_GETSTATUS return value 2012-06-28 20:40:56 +02:00
xen Five bug-fixes: 2012-06-15 17:17:15 -07:00
zorro
Kconfig Staging tree pull request for 3.5-rc1 2012-05-22 16:34:21 -07:00
Makefile arm-soc: driver specific updates 2012-05-26 12:22:27 -07:00