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From: Manish Sharma <manish.sharmajee75@gmail.com>
To: dev@dpdk.org
Subject: [dpdk-dev] rte_memcpy
Date: Mon, 24 May 2021 14:19:21 +0530	[thread overview]
Message-ID: <CAOT2AHVSfmYi3rB4cnXwi-NDf7hG8_p97G5FLnD0-PxaL637MA@mail.gmail.com> (raw)

I am looking at the source for rte_memcpy (this is a discussion only for
x64-64)

For one of the cases, when aligned correctly, it uses

/**
 * Copy 64 bytes from one location to another,
 * locations should not overlap.
 */
static __rte_always_inline void
rte_mov64(uint8_t *dst, const uint8_t *src)
{
        __m512i zmm0;

        zmm0 = _mm512_loadu_si512((const void *)src);
        _mm512_storeu_si512((void *)dst, zmm0);
}

I had some questions about this:

1. What I dont see is any use of x86 fence(rmb,wmb) instructions. Is that
not required in this case and if not, why isnt it needed?

2. Are the  mm512_loadu_si512 and  _mm512_storeu_si512 non temporal?

3. Why isn't the code using  stream variants, _mm512_stream_load_si512 and
friends?

4. Do the _mm512_stream_load_si512 need fence instructions?

TIA,
Manish

             reply	other threads:[~2021-05-24  8:49 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-24  8:49 Manish Sharma [this message]
2021-05-24 18:13 ` [dpdk-dev] rte_memcpy - fence and stream Manish Sharma
2021-05-25  9:20   ` Bruce Richardson
2021-05-27 15:49     ` Morten Brørup
2021-05-27 16:25       ` Bruce Richardson
2021-05-27 17:09         ` Manish Sharma
2021-05-27 17:22           ` Bruce Richardson
2021-05-27 18:15             ` Morten Brørup
2021-06-22 21:55               ` Morten Brørup

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