From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1F13AC4332F for ; Mon, 12 Dec 2022 09:38:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231950AbiLLJih (ORCPT ); Mon, 12 Dec 2022 04:38:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57480 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231565AbiLLJi1 (ORCPT ); Mon, 12 Dec 2022 04:38:27 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D187A293; Mon, 12 Dec 2022 01:38:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=MZjvdGsr7OQyc+WN8WWS9d9aoiScOd7BDAvol982NI4=; b=SkUFdD4cXgZJin1CbKwdnZF3+v PBy4SMek1/mx0YdhUrmZOuxhrW66sJsha6VNlvlYR6lP750n4SDvcUpjma6D/jzV6ml00fLJpAkqE +d6vWonMKNYt8wY8LEqU0CjedKmWBgep0wJlQzoMJSpgAjXWWOYk9PxJjccEDr1kmnYzxSdXxeIpq w+WKKemqKSewFB7/mRMKSquRCK5cxfif/0+sFEI7hPZXxAme5xNciZY1/iPoCNF3dZhL7w3LuD3Ok cMXuqgNsh6nNXzdnoTKfDWf/04vlzQVTy4fRKcMk7dxtwB6Bow3/ZQIR6mU3lcCgjiXH2F60XL/by oBkUUzXQ==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1p4fG7-00Atcl-P7; Mon, 12 Dec 2022 09:38:03 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4D762300137; Mon, 12 Dec 2022 10:37:51 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 0D6C620AF3509; Mon, 12 Dec 2022 10:37:51 +0100 (CET) Date: Mon, 12 Dec 2022 10:37:50 +0100 From: Peter Zijlstra To: Tejun Heo Cc: torvalds@linux-foundation.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, joshdon@google.com, brho@google.com, pjt@google.com, derkling@google.com, haoluo@google.com, dvernet@meta.com, dschatzberg@meta.com, dskarlat@cs.cmu.edu, riel@surriel.com, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCHSET RFC] sched: Implement BPF extensible scheduler class Message-ID: References: <20221130082313.3241517-1-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221130082313.3241517-1-tj@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 29, 2022 at 10:22:42PM -1000, Tejun Heo wrote: > Core scheduling is an example of a feature that took a significant amount of > time and effort to integrate into the kernel. Mostly because I dropped it on the floor once I heard about MDS. That made me lose interest entirely. The only reason it eventually happened was ChromeOS (Joel) pushing for it again. > Part of the difficulty with core > scheduling was the inherent mismatch in abstraction between the desire to > perform core-wide scheduling, and the per-cpu design of the kernel scheduler. Not really; the main difficultly was due to me wanting to do it outside of the scheduling classes so that it fundamentally covers all of them. Doing it inside a class (say CFS) would've made it significantly simpler. > This caused issues, for example ensuring proper fairness between the > independent runqueues of SMT siblings. Inter-runqueue fairness is a known issue of CFS and quite independent of core scheduling. Anyway, I hate all of this. Linus NAK'ed loadable schedulers a number of times in the past and this is just that again -- with the extra downside of the whole BPF thing on top :/ You look to be exposing a ton of stuff I've so far even refused tracepoints for :-( Anyway, I'm just back from a heavy dose of Covid and still taking it easy, but I'll go read through the whole thing, hopefully I'll finish before vanishing again for the x-mas break.