I noticed ksm spending quite a lot of time in memcmp on a large
KVM box. The current memcmp loop is very unoptimised - byte at a
time compares with no loop unrolling. We can do much much better.
Optimise the loop in a few ways:
- Unroll the byte at a time loop
- For large (at least 32 byte) comparisons that are also 8 byte
aligned, use an unrolled modulo scheduled loop using 8 byte
loads. This is similar to our glibc memcmp.
A simple microbenchmark testing 10000000 iterations of an 8192 byte
memcmp was used to measure the performance:
baseline: 29.93 s
modified: 1.70 s
Just over 17x faster.
v2: Incorporated some suggestions from Segher:
- Use andi. instead of rdlicl.
- Convert bdnzt eq, to bdnz. It's just duplicating the earlier compare
and was a relic from a previous version.
- Don't use cr5, we have plans to use that CR field for fast local
atomics.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
I noticed __clear_user high up in a profile of one of my RAID stress
tests. The testcase was doing a dd from /dev/zero which ends up
calling __clear_user.
__clear_user is basically a loop with a single 4 byte store which
is horribly slow. We can do much better by aligning the desination
and doing 32 bytes of 8 byte stores in a loop.
The following testcase was used to verify the patch:
http://ozlabs.org/~anton/junkcode/stress_clear_user.c
To show the improvement in performance I ran a dd from /dev/zero
to /dev/null on a POWER7 box:
Before:
# dd if=/dev/zero of=/dev/null bs=1M count=10000
10485760000 bytes (10 GB) copied, 3.72379 s, 2.8 GB/s
After:
# time dd if=/dev/zero of=/dev/null bs=1M count=10000
10485760000 bytes (10 GB) copied, 0.728318 s, 14.4 GB/s
Over 5x faster.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This is much the same as for SPARC except that we can do the find_zero()
function more efficiently using the count-leading-zeroes instructions.
Tested on 32-bit and 64-bit PowerPC.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The powerpc strncmp implementation does not correctly handle a zero
length, despite the claim in 0119536cd3
(Add hand-coded assembly strcmp).
Additionally, all the length arguments are size_t, not int, so use
PPC_LCMPI and eq instead of cmpwi and le throughout.
Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Commit 0119536c, which added the assembly version of strncmp to
powerpc, mentions that it adds two instructions to the version from
boot/string.S to allow it to handle len=0. Unfortunately, it doesn't
always return 0 when that is the case. The length is passed in r5, but
the return value is passed back in r3. In certain cases, this will
happen to work. Otherwise it will pass back the address of the first
string as the return value.
This patch lifts the len <= 0 handling code from memcpy to handle that
case.
Reported by: Christian_Sellars@symantec.com
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
CC: <stable@kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Replace ifdef clutter with the PPC_LONG and PPC_LONG_ALIGN macros
for readability.
No change to the generated code.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
We have an assembly version of strncmp for the bootwrapper, but not
for the kernel, so we end up using the C version in the kernel. This
takes the strncmp code from the bootup and copies it to the kernel
proper, adding two instructions so it copes correctly with len==0.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Now that the register names and bit definitions are all in reg.h,
use that instead of processor.h in assembly code in a few places.
Signed-off-by: Paul Mackerras <paulus@samba.org>
This creates the directory structure under arch/powerpc and a bunch
of Kconfig files. It does a first-cut merge of arch/powerpc/mm,
arch/powerpc/lib and arch/powerpc/platforms/powermac. This is enough
to build a 32-bit powermac kernel with ARCH=powerpc.
For now we are getting some unmerged files from arch/ppc/kernel and
arch/ppc/syslib, or arch/ppc64/kernel. This makes some minor changes
to files in those directories and files outside arch/powerpc.
The boot directory is still not merged. That's going to be interesting.
Signed-off-by: Paul Mackerras <paulus@samba.org>
