As suggested by Peter Anvin.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: H . Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Apparently 'byts' should be 'bytes'.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: H . Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
movs instruction will combine data to accelerate moving data,
however we need to concern two cases about it.
1. movs instruction need long lantency to startup,
so here we use general mov instruction to copy data.
2. movs instruction is not good for unaligned case,
even if src offset is 0x10, dest offset is 0x0,
we avoid and handle the case by general mov instruction.
Signed-off-by: Ma Ling <ling.ma@intel.com>
LKML-Reference: <1284664360-6138-1-git-send-email-ling.ma@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
All read operations after allocation stage can run speculatively,
all write operation will run in program order, and if addresses are
different read may run before older write operation, otherwise wait
until write commit. However CPU don't check each address bit,
so read could fail to recognize different address even they
are in different page.For example if rsi is 0xf004, rdi is 0xe008,
in following operation there will generate big performance latency.
1. movq (%rsi), %rax
2. movq %rax, (%rdi)
3. movq 8(%rsi), %rax
4. movq %rax, 8(%rdi)
If %rsi and rdi were in really the same meory page, there are TRUE
read-after-write dependence because instruction 2 write 0x008 and
instruction 3 read 0x00c, the two address are overlap partially.
Actually there are in different page and no any issues,
but without checking each address bit CPU could think they are
in the same page, and instruction 3 have to wait for instruction 2
to write data into cache from write buffer, then load data from cache,
the cost time read spent is equal to mfence instruction. We may avoid it by
tuning operation sequence as follow.
1. movq 8(%rsi), %rax
2. movq %rax, 8(%rdi)
3. movq (%rsi), %rax
4. movq %rax, (%rdi)
Instruction 3 read 0x004, instruction 2 write address 0x010, no any
dependence. At last on Core2 we gain 1.83x speedup compared with
original instruction sequence. In this patch we first handle small
size(less 20bytes), then jump to different copy mode. Based on our
micro-benchmark small bytes from 1 to 127 bytes, we got up to 2X
improvement, and up to 1.5X improvement for 1024 bytes on Corei7. (We
use our micro-benchmark, and will do further test according to your
requirment)
Signed-off-by: Ma Ling <ling.ma@intel.com>
LKML-Reference: <1277753065-18610-1-git-send-email-ling.ma@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
memmove() allow source and destination address to be overlap, but
there is no such limitation for memcpy(). Therefore, explicitly
implement memmove() in both the forwards and backward directions, to
give us the ability to optimize memcpy().
Signed-off-by: Ma Ling <ling.ma@intel.com>
LKML-Reference: <C10D3FB0CD45994C8A51FEC1227CE22F0E483AD86A@shsmsx502.ccr.corp.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
