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b=ugDahyl4HvC44LCuo7pbGdvpICtbWEvnh+OrxFbkLqQbMVd+2uN1xW4IhSvFQeDzMulvDpex27DJLRKV6BJ9bxi/ird84AFfhocVQCQptrYykM1YALHVp9fQkV1+gmynyVrLXBf0qnWzkTgkugxF4H0NlKmhAJHYiSlUBnzRKLE= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from PH8PR12MB6914.namprd12.prod.outlook.com (2603:10b6:510:1cb::21) by CH3PR12MB8233.namprd12.prod.outlook.com (2603:10b6:610:129::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.406.7; Wed, 9 Sep 2026 13:19:37 +0000 Received: from PH8PR12MB6914.namprd12.prod.outlook.com ([fe80::2893:177a:72b0:6000]) by PH8PR12MB6914.namprd12.prod.outlook.com ([fe80::2893:177a:72b0:6000%7]) with mapi id 15.21.0406.005; Wed, 9 Sep 2026 13:19:37 +0000 Message-ID: <76dba935-1052-4fa9-a70c-16cecdfd12c8@amd.com> Date: Wed, 9 Sep 2026 08:19:32 -0500 User-Agent: Mozilla Thunderbird Beta Subject: Re: Cache-aware scheduling does not work well with amd big/little cores Content-Language: en-US To: Klaus Kusche , Tim Chen , "Chen, Yu C" Cc: "Badole, Vishal" , Peter Zijlstra , linux-kernel@vger.kernel.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , platform-driver-x86@vger.kernel.org, K Prateek Nayak , ricardo.neri@intel.com References: <2180ea5a-eb28-4152-8d4d-cd00b0c24b2e@computerix.info> <8064e1d8-b51c-48e5-a312-8c31581991f5@amd.com> <369d0bbb-db7a-4f86-bee2-332d5295c452@computerix.info> <406a5c407bbe60cafc24f715e089f5552a0791f9.camel@linux.intel.com> <14630984-9287-4454-b52f-3a1e526e1fdf@computerix.info> <3cb5cbdb227bee0b822f1550e10659faadd77a3d.camel@linux.intel.com> From: Mario Limonciello In-Reply-To: Content-Type: text/plain; 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You mentioned later the result for (b) >> and (c) are about the same with or without the patch >> exposing debugfs (commit c1e7fe5e75ed11fa85368e5a186472afd3858f3a >> Mario mentioned in another mail). >> But here you say the result is much worse without Mario's patch. >> Is Mario's patch the one above or some other patch? > > The with/without patch in (b) and (c) > refers to the patch you sent on 31/08/2026 > ( https://lore.kernel.org/lkml/20260825174112.2580942-1-tim.c.chen@linux.intel.com/ ), > not to Mario's patch. > Just to clarify Mario's patch in this context refers to the fix to ITMT/debugfs fixes as Klaus doesn't nominally enable debugfs in Kconfig: eaece4849991d62fcd6f46637c55dcce00e25d70 >>> because I use kernels without debugfs, >>> so big/little scheduling is off without the patch). >>> >>> Results: >>> >>> There is no significant difference between b) and c) >>> (<= 1 % wallclock time) >> >> Yes, I don't expect difference between (b) and (c). My >> understanding is the patch in question is to only >> expose the default cache aware parameters via debugfs >> but don't acutally change them. >> >>> Sometimes b) is better, sometimes c) is better, >>> I'd say the differences are below the accuracy of my tests. >>> >>> But a) was reproducibly better than b) and c) >>> w.r.t. wallclock time: 2-2.6 % >>> It was also very slightly better w.r.t. total kernel CPU seconds. >>> The results w.r.t. total usermode CPU seconds varied too much. >>> (I always ran the application build twice, >>> and for all a), b) and c), the second run consumed >>> significantly more usermode CPU seconds, >>> but took a little less wallclock time - I don't know why). >> >> Will have to look around to see if we have some similar CPUs >> as HX-370. My understanding is that the 4 big cores are in >> one L3 and the 8 small cores are in another L3. > > Yes, as far as I know, it has 16 MB L3 cache for the 4 big cores > and 8 MB L3 cache for the 8 little cores. > >> BTW, we have also found two issues with the active load balance >> paths for CAS that need fixes. You may want to add those patches >> and see if they are helpful to improve things. > > Most likely not within the next few days. > I'm still on holiday and quite busy: > Ars Electronica Festival in Linz. > >> Active load balance fixes: >> https://lore.kernel.org/lkml/20260903020656.3793626-1-wanglu.priv@gmail.com/ >> https://lore.kernel.org/lkml/2b0a35122ee615c6fa51076e5d79330e633755ac.camel@linux.intel.com/ >