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Message-ID: <a9ce9ea2-9e5d-0e56-d980-5dedd087f62d@kernel.org>
Date: Thu, 30 Sep 2021 12:43:50 -0700
From: Vineet Gupta <vgupta@...nel.org>
To: Matteo Croce <mcroce@...ux.microsoft.com>,
Guo Ren <guoren@...nel.org>
Cc: linux-riscv <linux-riscv@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Atish Patra <atish.patra@....com>,
Emil Renner Berthing <kernel@...il.dk>,
Akira Tsukamoto <akira.tsukamoto@...il.com>,
Drew Fustini <drew@...gleboard.org>,
Bin Meng <bmeng.cn@...il.com>,
David Laight <David.Laight@...lab.com>,
Christoph Hellwig <hch@....de>,
Philipp Tomsich <philipp.tomsich@...ll.eu>
Subject: Re: [PATCH v5 1/3] riscv: optimized memcpy
On 9/29/21 6:36 PM, Matteo Croce wrote:
> On Thu, Sep 30, 2021 at 3:25 AM Guo Ren <guoren@...nel.org> wrote:
>>
>> On Thu, Sep 30, 2021 at 1:22 AM Matteo Croce <mcroce@...ux.microsoft.com> wrote:
>>>
>>> From: Matteo Croce <mcroce@...rosoft.com>
>>>
>>> Write a C version of memcpy() which uses the biggest data size allowed,
>>> without generating unaligned accesses.
>>>
>>> The procedure is made of three steps:
>>> First copy data one byte at time until the destination buffer is aligned
>>> to a long boundary.
>>> Then copy the data one long at time shifting the current and the next u8
>>> to compose a long at every cycle.
>>> Finally, copy the remainder one byte at time.
>>>
>>> On a BeagleV, the TCP RX throughput increased by 45%:
>>>
>>> before:
>>>
>>> $ iperf3 -c beaglev
>>> Connecting to host beaglev, port 5201
>>> [ 5] local 192.168.85.6 port 44840 connected to 192.168.85.48 port 5201
>>> [ ID] Interval Transfer Bitrate Retr Cwnd
>>> [ 5] 0.00-1.00 sec 76.4 MBytes 641 Mbits/sec 27 624 KBytes
>>> [ 5] 1.00-2.00 sec 72.5 MBytes 608 Mbits/sec 0 708 KBytes
>>> [ 5] 2.00-3.00 sec 73.8 MBytes 619 Mbits/sec 10 451 KBytes
>>> [ 5] 3.00-4.00 sec 72.5 MBytes 608 Mbits/sec 0 564 KBytes
>>> [ 5] 4.00-5.00 sec 73.8 MBytes 619 Mbits/sec 0 658 KBytes
>>> [ 5] 5.00-6.00 sec 73.8 MBytes 619 Mbits/sec 14 522 KBytes
>>> [ 5] 6.00-7.00 sec 73.8 MBytes 619 Mbits/sec 0 621 KBytes
>>> [ 5] 7.00-8.00 sec 72.5 MBytes 608 Mbits/sec 0 706 KBytes
>>> [ 5] 8.00-9.00 sec 73.8 MBytes 619 Mbits/sec 20 580 KBytes
>>> [ 5] 9.00-10.00 sec 73.8 MBytes 619 Mbits/sec 0 672 KBytes
>>> - - - - - - - - - - - - - - - - - - - - - - - - -
>>> [ ID] Interval Transfer Bitrate Retr
>>> [ 5] 0.00-10.00 sec 736 MBytes 618 Mbits/sec 71 sender
>>> [ 5] 0.00-10.01 sec 733 MBytes 615 Mbits/sec receiver
>>>
>>> after:
>>>
>>> $ iperf3 -c beaglev
>>> Connecting to host beaglev, port 5201
>>> [ 5] local 192.168.85.6 port 44864 connected to 192.168.85.48 port 5201
>>> [ ID] Interval Transfer Bitrate Retr Cwnd
>>> [ 5] 0.00-1.00 sec 109 MBytes 912 Mbits/sec 48 559 KBytes
>>> [ 5] 1.00-2.00 sec 108 MBytes 902 Mbits/sec 0 690 KBytes
>>> [ 5] 2.00-3.00 sec 106 MBytes 891 Mbits/sec 36 396 KBytes
>>> [ 5] 3.00-4.00 sec 108 MBytes 902 Mbits/sec 0 567 KBytes
>>> [ 5] 4.00-5.00 sec 106 MBytes 891 Mbits/sec 0 699 KBytes
>>> [ 5] 5.00-6.00 sec 106 MBytes 891 Mbits/sec 32 414 KBytes
>>> [ 5] 6.00-7.00 sec 106 MBytes 891 Mbits/sec 0 583 KBytes
>>> [ 5] 7.00-8.00 sec 106 MBytes 891 Mbits/sec 0 708 KBytes
>>> [ 5] 8.00-9.00 sec 106 MBytes 891 Mbits/sec 28 433 KBytes
>>> [ 5] 9.00-10.00 sec 108 MBytes 902 Mbits/sec 0 591 KBytes
>>> - - - - - - - - - - - - - - - - - - - - - - - - -
>>> [ ID] Interval Transfer Bitrate Retr
>>> [ 5] 0.00-10.00 sec 1.04 GBytes 897 Mbits/sec 144 sender
>>> [ 5] 0.00-10.01 sec 1.04 GBytes 894 Mbits/sec receiver
>>>
>>> And the decreased CPU time of the memcpy() is observable with perf top.
>>> This is the `perf top -Ue task-clock` output when doing the test:
>>>
>>> before:
>>>
>>> Overhead Shared O Symbol
>>> 42.22% [kernel] [k] memcpy
>>> 35.00% [kernel] [k] __asm_copy_to_user
>>> 3.50% [kernel] [k] sifive_l2_flush64_range
>>> 2.30% [kernel] [k] stmmac_napi_poll_rx
>>> 1.11% [kernel] [k] memset
>>>
>>> after:
>>>
>>> Overhead Shared O Symbol
>>> 45.69% [kernel] [k] __asm_copy_to_user
>>> 29.06% [kernel] [k] memcpy
>>> 4.09% [kernel] [k] sifive_l2_flush64_range
>>> 2.77% [kernel] [k] stmmac_napi_poll_rx
>>> 1.24% [kernel] [k] memset
>>>
>>> Signed-off-by: Matteo Croce <mcroce@...rosoft.com>
>>> Reported-by: kernel test robot <lkp@...el.com>
>>> ---
>>> arch/riscv/include/asm/string.h | 8 ++-
>>> arch/riscv/kernel/riscv_ksyms.c | 2 -
>>> arch/riscv/lib/Makefile | 2 +-
>>> arch/riscv/lib/memcpy.S | 108 --------------------------------
>>> arch/riscv/lib/string.c | 90 ++++++++++++++++++++++++++
>>> 5 files changed, 97 insertions(+), 113 deletions(-)
>>> delete mode 100644 arch/riscv/lib/memcpy.S
>>> create mode 100644 arch/riscv/lib/string.c
>>>
>>> diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
>>> index 909049366555..6b5d6fc3eab4 100644
>>> --- a/arch/riscv/include/asm/string.h
>>> +++ b/arch/riscv/include/asm/string.h
>>> @@ -12,9 +12,13 @@
>>> #define __HAVE_ARCH_MEMSET
>>> extern asmlinkage void *memset(void *, int, size_t);
>>> extern asmlinkage void *__memset(void *, int, size_t);
>>> +
>>> +#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
>> What's the problem with the -O3 & -Os? If the user uses
>> CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 that will cause bad performance
>> for memcpy?
>> Seems asm version is more compatible?
>>
>>> #define __HAVE_ARCH_MEMCPY
>>> -extern asmlinkage void *memcpy(void *, const void *, size_t);
>>> -extern asmlinkage void *__memcpy(void *, const void *, size_t);
>>> +extern void *memcpy(void *dest, const void *src, size_t count);
>>> +extern void *__memcpy(void *dest, const void *src, size_t count);
>>> +#endif
>>> +
>>> #define __HAVE_ARCH_MEMMOVE
>>> extern asmlinkage void *memmove(void *, const void *, size_t);
>>> extern asmlinkage void *__memmove(void *, const void *, size_t);
>>> diff --git a/arch/riscv/kernel/riscv_ksyms.c b/arch/riscv/kernel/riscv_ksyms.c
>>> index 5ab1c7e1a6ed..3f6d512a5b97 100644
>>> --- a/arch/riscv/kernel/riscv_ksyms.c
>>> +++ b/arch/riscv/kernel/riscv_ksyms.c
>>> @@ -10,8 +10,6 @@
>>> * Assembly functions that may be used (directly or indirectly) by modules
>>> */
>>> EXPORT_SYMBOL(memset);
>>> -EXPORT_SYMBOL(memcpy);
>>> EXPORT_SYMBOL(memmove);
>>> EXPORT_SYMBOL(__memset);
>>> -EXPORT_SYMBOL(__memcpy);
>>> EXPORT_SYMBOL(__memmove);
>>> diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
>>> index 25d5c9664e57..2ffe85d4baee 100644
>>> --- a/arch/riscv/lib/Makefile
>>> +++ b/arch/riscv/lib/Makefile
>>> @@ -1,9 +1,9 @@
>>> # SPDX-License-Identifier: GPL-2.0-only
>>> lib-y += delay.o
>>> -lib-y += memcpy.o
>>> lib-y += memset.o
>>> lib-y += memmove.o
>>> lib-$(CONFIG_MMU) += uaccess.o
>>> lib-$(CONFIG_64BIT) += tishift.o
>>> +lib-$(CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE) += string.o
>>>
>>> obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
>>> diff --git a/arch/riscv/lib/memcpy.S b/arch/riscv/lib/memcpy.S
>>> deleted file mode 100644
>>> index 51ab716253fa..000000000000
>>> --- a/arch/riscv/lib/memcpy.S
>>> +++ /dev/null
>>> @@ -1,108 +0,0 @@
>>> -/* SPDX-License-Identifier: GPL-2.0-only */
>>> -/*
>>> - * Copyright (C) 2013 Regents of the University of California
>>> - */
>>> -
>>> -#include <linux/linkage.h>
>>> -#include <asm/asm.h>
>>> -
>>> -/* void *memcpy(void *, const void *, size_t) */
>>> -ENTRY(__memcpy)
>>> -WEAK(memcpy)
>>> - move t6, a0 /* Preserve return value */
>>> -
>>> - /* Defer to byte-oriented copy for small sizes */
>>> - sltiu a3, a2, 128
>>> - bnez a3, 4f
>>> - /* Use word-oriented copy only if low-order bits match */
>>> - andi a3, t6, SZREG-1
>>> - andi a4, a1, SZREG-1
>>> - bne a3, a4, 4f
>>> -
>>> - beqz a3, 2f /* Skip if already aligned */
>>> - /*
>>> - * Round to nearest double word-aligned address
>>> - * greater than or equal to start address
>>> - */
>>> - andi a3, a1, ~(SZREG-1)
>>> - addi a3, a3, SZREG
>>> - /* Handle initial misalignment */
>>> - sub a4, a3, a1
>>> -1:
>>> - lb a5, 0(a1)
>>> - addi a1, a1, 1
>>> - sb a5, 0(t6)
>>> - addi t6, t6, 1
>>> - bltu a1, a3, 1b
>>> - sub a2, a2, a4 /* Update count */
>>> -
>>> -2:
>>> - andi a4, a2, ~((16*SZREG)-1)
>>> - beqz a4, 4f
>>> - add a3, a1, a4
>>> -3:
>>> - REG_L a4, 0(a1)
>>> - REG_L a5, SZREG(a1)
>>> - REG_L a6, 2*SZREG(a1)
>>> - REG_L a7, 3*SZREG(a1)
>>> - REG_L t0, 4*SZREG(a1)
>>> - REG_L t1, 5*SZREG(a1)
>>> - REG_L t2, 6*SZREG(a1)
>>> - REG_L t3, 7*SZREG(a1)
>>> - REG_L t4, 8*SZREG(a1)
>>> - REG_L t5, 9*SZREG(a1)
>>> - REG_S a4, 0(t6)
>>> - REG_S a5, SZREG(t6)
>>> - REG_S a6, 2*SZREG(t6)
>>> - REG_S a7, 3*SZREG(t6)
>>> - REG_S t0, 4*SZREG(t6)
>>> - REG_S t1, 5*SZREG(t6)
>>> - REG_S t2, 6*SZREG(t6)
>>> - REG_S t3, 7*SZREG(t6)
>>> - REG_S t4, 8*SZREG(t6)
>>> - REG_S t5, 9*SZREG(t6)
>>> - REG_L a4, 10*SZREG(a1)
>>> - REG_L a5, 11*SZREG(a1)
>>> - REG_L a6, 12*SZREG(a1)
>>> - REG_L a7, 13*SZREG(a1)
>>> - REG_L t0, 14*SZREG(a1)
>>> - REG_L t1, 15*SZREG(a1)
>>> - addi a1, a1, 16*SZREG
>>> - REG_S a4, 10*SZREG(t6)
>>> - REG_S a5, 11*SZREG(t6)
>>> - REG_S a6, 12*SZREG(t6)
>>> - REG_S a7, 13*SZREG(t6)
>>> - REG_S t0, 14*SZREG(t6)
>>> - REG_S t1, 15*SZREG(t6)
>>> - addi t6, t6, 16*SZREG
>>> - bltu a1, a3, 3b
>>> - andi a2, a2, (16*SZREG)-1 /* Update count */
>>> -
>>> -4:
>>> - /* Handle trailing misalignment */
>>> - beqz a2, 6f
>>> - add a3, a1, a2
>>> -
>>> - /* Use word-oriented copy if co-aligned to word boundary */
>>> - or a5, a1, t6
>>> - or a5, a5, a3
>>> - andi a5, a5, 3
>>> - bnez a5, 5f
>>> -7:
>>> - lw a4, 0(a1)
>>> - addi a1, a1, 4
>>> - sw a4, 0(t6)
>>> - addi t6, t6, 4
>>> - bltu a1, a3, 7b
>>> -
>>> - ret
>>> -
>>> -5:
>>> - lb a4, 0(a1)
>>> - addi a1, a1, 1
>>> - sb a4, 0(t6)
>>> - addi t6, t6, 1
>>> - bltu a1, a3, 5b
>>> -6:
>>> - ret
>>> -END(__memcpy)
>>> diff --git a/arch/riscv/lib/string.c b/arch/riscv/lib/string.c
>>> new file mode 100644
>>> index 000000000000..bfc912ee23f8
>>> --- /dev/null
>>> +++ b/arch/riscv/lib/string.c
>>> @@ -0,0 +1,90 @@
>>> +// SPDX-License-Identifier: GPL-2.0-only
>>> +/*
>>> + * String functions optimized for hardware which doesn't
>>> + * handle unaligned memory accesses efficiently.
>>> + *
>>> + * Copyright (C) 2021 Matteo Croce
>>> + */
>>> +
>>> +#include <linux/types.h>
>>> +#include <linux/module.h>
>>> +
>>> +/* Minimum size for a word copy to be convenient */
>>> +#define BYTES_LONG sizeof(long)
>>> +#define WORD_MASK (BYTES_LONG - 1)
>>> +#define MIN_THRESHOLD (BYTES_LONG * 2)
>>> +
>>> +/* convenience union to avoid cast between different pointer types */
>>> +union types {
>>> + u8 *as_u8;
>>> + unsigned long *as_ulong;
>>> + uintptr_t as_uptr;
>>> +};
>>> +
>>> +union const_types {
>>> + const u8 *as_u8;
>>> + unsigned long *as_ulong;
>>> + uintptr_t as_uptr;
>>> +};
>>> +
>>> +void *__memcpy(void *dest, const void *src, size_t count)
>> How about using __attribute__((optimize("-O2"))) here to replace your
>> previous "#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE"?
>>
>>> +{
>>> + union const_types s = { .as_u8 = src };
>>> + union types d = { .as_u8 = dest };
>>> + int distance = 0;
>>> +
>>> + if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) {
>>> + if (count < MIN_THRESHOLD)
>>> + goto copy_remainder;
>>> +
>>> + /* Copy a byte at time until destination is aligned. */
>>> + for (; d.as_uptr & WORD_MASK; count--)
>>> + *d.as_u8++ = *s.as_u8++;
>>> +
>>> + distance = s.as_uptr & WORD_MASK;
>>> + }
>>> +
>>> + if (distance) {
>>> + unsigned long last, next;
>>> +
>>> + /*
>>> + * s is distance bytes ahead of d, and d just reached
>>> + * the alignment boundary. Move s backward to word align it
>>> + * and shift data to compensate for distance, in order to do
>>> + * word-by-word copy.
>>> + */
>>> + s.as_u8 -= distance;
>>> +
>>> + next = s.as_ulong[0];
>>> + for (; count >= BYTES_LONG; count -= BYTES_LONG) {
>>> + last = next;
>>> + next = s.as_ulong[1];
>>> +
>>> + d.as_ulong[0] = last >> (distance * 8) |
>>> + next << ((BYTES_LONG - distance) * 8);
>>> +
>>> + d.as_ulong++;
>>> + s.as_ulong++;
>>> + }
>>> +
>>> + /* Restore s with the original offset. */
>>> + s.as_u8 += distance;
>>> + } else {
>>> + /*
>>> + * If the source and dest lower bits are the same, do a simple
>>> + * 32/64 bit wide copy.
>>> + */
>>> + for (; count >= BYTES_LONG; count -= BYTES_LONG)
>>> + *d.as_ulong++ = *s.as_ulong++;
>>> + }
>>> +
>>> +copy_remainder:
>>> + while (count--)
>>> + *d.as_u8++ = *s.as_u8++;
>>> +
>>> + return dest;
>>> +}
>>> +EXPORT_SYMBOL(__memcpy);
>>> +
>>> +void *memcpy(void *dest, const void *src, size_t count) __weak __alias(__memcpy);
>>> +EXPORT_SYMBOL(memcpy);
>>> --
>>> 2.31.1
>>>
>>
>>
>> --
>> Best Regards
>> Guo Ren
>>
>> ML: https://lore.kernel.org/linux-csky/
>
> If CONFIG_CC_OPTIMIZE_FOR_SIZE I fallback to the generic
> implementations, which are very small.
> It's just an optimization to save more space when -Os is used.
>
> CC_OPTIMIZE_FOR_PERFORMANCE_O3 is ARC specific.
It is not. Its just that for ARC I've used -O3 as default. Historically
for compilers at the time some architecture had issues with -O3 builds
and/or compiler would inline more. But nothing in -O3 is specific to ARC.
BTW off topic (but relevant to this patchset), I strongly feel that
routines like memset/memcpy are better coded in assembly for really
water tight instruction scheduling and ease of further optimizing (e.g.
use of CMO.zero etc as experimented by Philipp). What is blocking you
from optimizing the asm version ? You are leaving the fate of these
critical routines in the hand of compiler - this can lead to performance
shenanigans on a big gcc upgrade.
-Vineet
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