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Date: Thu, 30 Sep 2021 03:36:01 +0200
From: Matteo Croce <mcroce@...ux.microsoft.com>
To: 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>
Subject: Re: [PATCH v5 1/3] riscv: optimized memcpy
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.
Regards,
--
per aspera ad upstream
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