Re: [EXT] [PATCH v8 3/3] spinlock: reimplement with atomic one-way barrier builtins

[Jerin Jacob Kollanukkaran <jerinj@marvell.com>]

On Fri, Mar 08, 2019 at 03:56:37PM +0800, Gavin Hu wrote:
> External Email
> 
> ----------------------------------------------------------------------
> The __sync builtin based implementation generates full memory barriers
> ('dmb ish') on Arm platforms. Using C11 atomic builtins to generate one way
> barriers.
> 
> Here is the assembly code of __sync_compare_and_swap builtin.
> __sync_bool_compare_and_swap(dst, exp, src);
>    0x000000000090f1b0 <+16>:    e0 07 40 f9 ldr x0, [sp, #8]
>    0x000000000090f1b4 <+20>:    e1 0f 40 79 ldrh    w1, [sp, #6]
>    0x000000000090f1b8 <+24>:    e2 0b 40 79 ldrh    w2, [sp, #4]
>    0x000000000090f1bc <+28>:    21 3c 00 12 and w1, w1, #0xffff
>    0x000000000090f1c0 <+32>:    03 7c 5f 48 ldxrh   w3, [x0]
>    0x000000000090f1c4 <+36>:    7f 00 01 6b cmp w3, w1
>    0x000000000090f1c8 <+40>:    61 00 00 54 b.ne    0x90f1d4
> <rte_atomic16_cmpset+52>  // b.any
>    0x000000000090f1cc <+44>:    02 fc 04 48 stlxrh  w4, w2, [x0]
>    0x000000000090f1d0 <+48>:    84 ff ff 35 cbnz    w4, 0x90f1c0
> <rte_atomic16_cmpset+32>
>    0x000000000090f1d4 <+52>:    bf 3b 03 d5 dmb ish
>    0x000000000090f1d8 <+56>:    e0 17 9f 1a cset    w0, eq  // eq = none
> 
> The benchmarking results showed constant improvements on all available
> platforms:
> 1. Cavium ThunderX2: 126% performance;
> 2. Hisilicon 1616: 30%;
> 3. Qualcomm Falkor: 13%;
> 4. Marvell ARMADA 8040 with A72 cores on macchiatobin: 3.7%
> 
> Here is the example test result on TX2:
> $sudo ./build/app/test -l 16-27 -- i
> RTE>>spinlock_autotest
> 
> *** spinlock_autotest without this patch ***
> Test with lock on 12 cores...
> Core [16] Cost Time = 53886 us
> Core [17] Cost Time = 53605 us
> Core [18] Cost Time = 53163 us
> Core [19] Cost Time = 49419 us
> Core [20] Cost Time = 34317 us
> Core [21] Cost Time = 53408 us
> Core [22] Cost Time = 53970 us
> Core [23] Cost Time = 53930 us
> Core [24] Cost Time = 53283 us
> Core [25] Cost Time = 51504 us
> Core [26] Cost Time = 50718 us
> Core [27] Cost Time = 51730 us
> Total Cost Time = 612933 us
> 
> *** spinlock_autotest with this patch ***
> Test with lock on 12 cores...
> Core [16] Cost Time = 18808 us
> Core [17] Cost Time = 29497 us
> Core [18] Cost Time = 29132 us
> Core [19] Cost Time = 26150 us
> Core [20] Cost Time = 21892 us
> Core [21] Cost Time = 24377 us
> Core [22] Cost Time = 27211 us
> Core [23] Cost Time = 11070 us
> Core [24] Cost Time = 29802 us
> Core [25] Cost Time = 15793 us
> Core [26] Cost Time = 7474 us
> Core [27] Cost Time = 29550 us
> Total Cost Time = 270756 us
> 
> In the tests on ThunderX2, with more cores contending, the performance gain
> was even higher, indicating the __atomic implementation scales up better
> than __sync.
> 
> Fixes: af75078fece3 ("first public release")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> Reviewed-by: Phil Yang <phil.yang@arm.com>
> Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>
> Reviewed-by: Steve Capper <Steve.Capper@arm.com>

Reviewed-by: Jerin Jacob <jerinj@marvell.com>