{"action":"created","issue":{"url":"https://api.github.com/repos/xianyi/OpenBLAS/issues/1627","repository_url":"https://api.github.com/repos/xianyi/OpenBLAS","labels_url":"https://api.github.com/repos/xianyi/OpenBLAS/issues/1627/labels{/name}","comments_url":"https://api.github.com/repos/xianyi/OpenBLAS/issues/1627/comments","events_url":"https://api.github.com/repos/xianyi/OpenBLAS/issues/1627/events","html_url":"https://github.com/xianyi/OpenBLAS/issues/1627","id":333736108,"node_id":"MDU6SXNzdWUzMzM3MzYxMDg=","number":1627,"title":"Intel Core i7 rounding issues? ","user":{"login":"ayounes-nviso","id":28561380,"node_id":"MDQ6VXNlcjI4NTYxMzgw","avatar_url":"https://avatars2.githubusercontent.com/u/28561380?v=4","gravatar_id":"","url":"https://api.github.com/users/ayounes-nviso","html_url":"https://github.com/ayounes-nviso","followers_url":"https://api.github.com/users/ayounes-nviso/followers","following_url":"https://api.github.com/users/ayounes-nviso/following{/other_user}","gists_url":"https://api.github.com/users/ayounes-nviso/gists{/gist_id}","starred_url":"https://api.github.com/users/ayounes-nviso/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/ayounes-nviso/subscriptions","organizations_url":"https://api.github.com/users/ayounes-nviso/orgs","repos_url":"https://api.github.com/users/ayounes-nviso/repos","events_url":"https://api.github.com/users/ayounes-nviso/events{/privacy}","received_events_url":"https://api.github.com/users/ayounes-nviso/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":2,"created_at":"2018-06-19T15:58:23Z","updated_at":"2018-06-20T07:27:30Z","closed_at":null,"author_association":"NONE","body":"Hi there,\r\n\r\nWe have a C++ implementation of MTCNN (a CNN based Face Detector) which uses GEMM and GEMV functions for some layer. \r\nOn some older Intel platforms or on Android (Arm32), we have the very same results using OpenBlas, BLIS or a pure CPU implementation.\r\n\r\nBut with a recent enough Intel platform we have slightly different results when using OpenBlas (latest master), about 2 pixels difference out of MTCNN.\r\n\r\nThe results are correct with:\r\n* Intel Core i7 9xx (Nehalem Class Core i7), gcc-6\r\n* ARM 32 bits (clang 6, Android NDK r17)\r\n\r\nThe results are slightly different with:\r\n* Intel(R) Core(TM) i7-6500U CPU @ 2.50GHz, gcc-6, 7 or 8\r\n* Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz,  gcc-6\r\n\r\nAny idea how we can fix this discrepancy?\r\n\r\nThanks in advance and best regards,\r\nAbdel"},"comment":{"url":"https://api.github.com/repos/xianyi/OpenBLAS/issues/comments/398651592","html_url":"https://github.com/xianyi/OpenBLAS/issues/1627#issuecomment-398651592","issue_url":"https://api.github.com/repos/xianyi/OpenBLAS/issues/1627","id":398651592,"node_id":"MDEyOklzc3VlQ29tbWVudDM5ODY1MTU5Mg==","user":{"login":"martin-frbg","id":6192365,"node_id":"MDQ6VXNlcjYxOTIzNjU=","avatar_url":"https://avatars0.githubusercontent.com/u/6192365?v=4","gravatar_id":"","url":"https://api.github.com/users/martin-frbg","html_url":"https://github.com/martin-frbg","followers_url":"https://api.github.com/users/martin-frbg/followers","following_url":"https://api.github.com/users/martin-frbg/following{/other_user}","gists_url":"https://api.github.com/users/martin-frbg/gists{/gist_id}","starred_url":"https://api.github.com/users/martin-frbg/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/martin-frbg/subscriptions","organizations_url":"https://api.github.com/users/martin-frbg/orgs","repos_url":"https://api.github.com/users/martin-frbg/repos","events_url":"https://api.github.com/users/martin-frbg/events{/privacy}","received_events_url":"https://api.github.com/users/martin-frbg/received_events","type":"User","site_admin":false},"created_at":"2018-06-20T07:27:30Z","updated_at":"2018-06-20T07:27:30Z","author_association":"COLLABORATOR","body":"Much of the recent improvement is in the multithreading code, so not cpu-specific. Worst case you could build with TARGET=NEHALEM to force it to use the Nehalem code on the more modern systems (NO_AVX2 will build for Sandybridge I think). It could certainly be that you hit a bug somewhere in the Haswell kernels, I hope tracing this to individual BLAS functions called by your code is not too hard."}}
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