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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BN6PR18MB1140.namprd18.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: d9af3b8f-fd8f-4f17-6924-08d8589a659a X-MS-Exchange-CrossTenant-originalarrivaltime: 14 Sep 2020 10:39:02.5391 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 70e1fb47-1155-421d-87fc-2e58f638b6e0 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: WWpb5WcxGAovZqK98NmhIVXisy0uNDwN15kSbXUminNwx/Qyb7zyagpQEYoWueJFchxDMZZ5lbqbQnzW5rMQuPJ8ujsFXyDCiqTATR7Bfzo= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR18MB2674 X-OriginatorOrg: marvell.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-09-14_02:2020-09-10, 2020-09-14 signatures=0 Subject: Re: [dpdk-dev] [PATCH] eal: add new prefetch0_write variant X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" >> >This commit adds a new rte_prefetch0_write() variant, suggests to >the >> >compiler to use a prefetch instruction with intention to write. As a >> >compiler builtin, the compiler can choose based on compilation >target >> >what the best implementation for this instruction is. >> >> Why not have the other variants too i.e. l2/l3/temporal store >prefetches too? > >Hi Pavan, > Hi Harry, (LTNS) >Are there architectures that actually implement those? Usually for a WB >mem store to complete, >the data must be present in L1 cache (on x86 at least), and that's what >the patch below with write0 achieves. ARM64 does supports all modes of store prefetch " is one of: PLD Prefetch for load, encoded in the "Rt<4:3>" field as 0b00. PLI Preload instructions, encoded in the "Rt<4:3>" field as 0b01. PST Prefetch for store, encoded in the "Rt<4:3>" field as 0b10. is one of: L1 Level 1 cache, encoded in the "Rt<2:1>" field as 0b00. L2 Level 2 cache, encoded in the "Rt<2:1>" field as 0b01. L3 Level 3 cache, encoded in the "Rt<2:1>" field as 0b10. is one of: KEEP Retained or temporal prefetch, allocated in the cache normally. Encode= d in the "Rt<0>" field as 0. STRM Streaming or non-temporal prefetch, for data that is used only once. E= ncoded in the "Rt<0>" field as 1. For more information on these prefetch " > >I'm against adding all the variants "just in case", it leads to API bloat, >and increases >cognitive load on the programmer. My expectation is that in 99% of >usage the prefetch >write instruction should target L1. > There is a use case when cache mode is write through and application is=20 pipelining work across cores sharing same L2 cluster. >Cheers, -Harry Regards, Pavan. > >> >Signed-off-by: Harry van Haaren >> > >> >--- >> > >> >The integer constants passed to the builtin are not available as >> >a #define value, and doing #defines just for this write variant >> >does not seems a nice solution to me... particularly for those using >> >IDEs where any #define value is auto-hinted for code-completion. >> > >> >--- >> > lib/librte_eal/include/generic/rte_prefetch.h | 16 >++++++++++++++++ >> > 1 file changed, 16 insertions(+) > >