From: Bruce Richardson Date: Thu, 14 Apr 2016 16:02:36 +0000 (+0100) Subject: i40e: improve performance of vector PMD X-Git-Tag: spdx-start~6955 X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=0b6493fbb0d9c4a368ee819ccf65601c0d03d515;p=dpdk.git i40e: improve performance of vector PMD An analysis of the i40e code using Intel® VTune™ Amplifier 2016 showed that the code was unexpectedly causing stalls due to "Loads blocked by Store Forwards". This can occur when a load from memory has to wait due to the prior store being to the same address, but being of a smaller size i.e. the stored value cannot be directly returned to the loader. [See ref: https://software.intel.com/en-us/node/544454] These stalls are due to the way in which the data_len values are handled in the driver. The lengths are extracted using vector operations, but those 16-bit lengths are then assigned using scalar operations i.e. 16-bit stores. These regular 16-bit stores actually have two effects in the code: * they cause the "Loads blocked by Store Forwards" issues reported * they also cause the previous loads in the RX function to actually be a load followed by a store to an address on the stack, because the 16-bit assignment can't be done to an xmm register. By converting the 16-bit store operations into a sequence of SSE blend operations, we can ensure that the descriptor loads only occur once, and avoid both the additional stores and loads from the stack, as well as the stalls due to the blocked loads. Signed-off-by: Bruce Richardson Acked-by: Zhe Tao --- diff --git a/drivers/net/i40e/i40e_rxtx_vec.c b/drivers/net/i40e/i40e_rxtx_vec.c index 1e2fadddc2..9f67f9d181 100644 --- a/drivers/net/i40e/i40e_rxtx_vec.c +++ b/drivers/net/i40e/i40e_rxtx_vec.c @@ -192,11 +192,7 @@ desc_to_olflags_v(__m128i descs[4], struct rte_mbuf **rx_pkts) static inline void desc_pktlen_align(__m128i descs[4]) { - __m128i pktlen0, pktlen1, zero; - union { - uint16_t e[4]; - uint64_t dword; - } vol; + __m128i pktlen0, pktlen1; /* mask everything except pktlen field*/ const __m128i pktlen_msk = _mm_set_epi32(PKTLEN_MASK, PKTLEN_MASK, @@ -206,18 +202,18 @@ desc_pktlen_align(__m128i descs[4]) pktlen1 = _mm_unpackhi_epi32(descs[1], descs[3]); pktlen0 = _mm_unpackhi_epi32(pktlen0, pktlen1); - zero = _mm_xor_si128(pktlen0, pktlen0); - pktlen0 = _mm_srli_epi32(pktlen0, PKTLEN_SHIFT); pktlen0 = _mm_and_si128(pktlen0, pktlen_msk); - pktlen0 = _mm_packs_epi32(pktlen0, zero); - vol.dword = _mm_cvtsi128_si64(pktlen0); - /* let the descriptor byte 15-14 store the pkt len */ - *((uint16_t *)&descs[0]+7) = vol.e[0]; - *((uint16_t *)&descs[1]+7) = vol.e[1]; - *((uint16_t *)&descs[2]+7) = vol.e[2]; - *((uint16_t *)&descs[3]+7) = vol.e[3]; + pktlen0 = _mm_packs_epi32(pktlen0, pktlen0); + + descs[3] = _mm_blend_epi16(descs[3], pktlen0, 0x80); + pktlen0 = _mm_slli_epi64(pktlen0, 16); + descs[2] = _mm_blend_epi16(descs[2], pktlen0, 0x80); + pktlen0 = _mm_slli_epi64(pktlen0, 16); + descs[1] = _mm_blend_epi16(descs[1], pktlen0, 0x80); + pktlen0 = _mm_slli_epi64(pktlen0, 16); + descs[0] = _mm_blend_epi16(descs[0], pktlen0, 0x80); } /*