> From: Burakov, Anatoly [mailto:anatoly.bura...@intel.com] > Sent: Thursday, 5 June 2025 11.29 > > On 6/4/2025 4:59 PM, Bruce Richardson wrote: > > On Fri, May 30, 2025 at 02:57:19PM +0100, Anatoly Burakov wrote: > >> Currently, for 32-byte descriptor format, only SSE instruction set > is > >> supported. Add implementation for AVX2 and AVX512 instruction sets. > Since > >> we are using Rx descriptor definitions from common code, we can just > use > >> the generic descriptor definition, as we only ever write the first > 16 bytes > >> of it, and the layout is always the same for that part. > >> > >> Signed-off-by: Anatoly Burakov <anatoly.bura...@intel.com> > >> --- > >> > > > > Like the idea. Feedback inline below. > > > > /Bruce > > > > <snip> > > >> - /** > >> - * merge 0 & 1, by casting 0 to 256-bit and inserting 1 > >> - * into the high lanes. Similarly for 2 & 3 > >> - */ > >> - const __m256i vaddr0_256 = _mm256_castsi128_si256(vaddr0); > >> - const __m256i vaddr2_256 = _mm256_castsi128_si256(vaddr2); > >> + const __m128i vaddr0 = _mm_loadu_si128((const __m128i > *)&mb0->buf_addr); > >> + const __m128i vaddr1 = _mm_loadu_si128((const __m128i > *)&mb1->buf_addr); > > > > Minor nit, but do we need to use unaligned loads here? The mbuf is > marked > > as cache-aligned, and buf_addr is the first field in it. > > It was like that in the original code I think (unless it was a > copypaste > error), but sure, I can make it aligned.
I wonder if the compiler emits a warning if it can detect that the address of an aligned load instruction is not aligned. As a safeguard against future mbuf changes, you could add a static_assert that the buf_addr field is properly aligned. PS: According to the Intel Intrinsics Guide [1], unaligned load appears to have the exact same performance as aligned load, so it shouldn't make a practical difference with current CPUs. But it might make a difference on future CPUs, and with no need for unaligned load, I'm also in favor of aligned load here. [1]: https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html
