From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1D3BF32D450 for ; Tue, 28 Oct 2025 14:37:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761662274; cv=none; b=V3mZQx2ceuLMgbLq0K+5iNHWEgFjU3vuRbsTZ+TRD8xb1oxT4MjTGL2rJGRADVZcFQqUDbdK6ENCiBsGBhRf4rQoCSv9UrWcfYCF0LyaQgaWhQdSFrnLqF1XuzNJ+DgrgFNOkgIkOmHVoP783QnFfErV+ciILWgSBWQsz4ct75w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761662274; c=relaxed/simple; bh=FNAqnDifNFBgyCPGedx8QMbyxN8hGtIjXzp5yiKuE6k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NblJpnjdfG6KX26bvVUQoFDnRHJxyvpKrh+i01+ohDgVpc406ry9V2Dv9FZ3KG/f+3wm8R0053lzpqlcq/iOs+ZsTj9HkFfDSlOidu99Sbe8qpBn9DBFHhrikubsq8eGvCaDmjnTtlFmvb6zvIE9jip9D8lnBKD9La3hkEk1TBo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=u6qGGxXO; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="u6qGGxXO" 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=FNAqnDifNFBgyCPGedx8QMbyxN8hGtIjXzp5yiKuE6k=; b=u6qGGxXOvKp4if2NLv6gwHx+nT iYFP+zcP9Gdda7WguxzfCcoXkb+jR2YrRJakVrOqABDkCQuZb55H0Mo1nqL88nhdHCIoHnbCEkpFP ZALa7oim7YFISGOHVyaAgMn/+enpJLAzWA+GogfdwZYyspb0w2CvKunuLPThpb97ZN6u3mQW4OZx0 VWEIVleRypD7CfA7aMCgdmykT9xK/SVbO7r3Z5scHYKCgkwedWMbbP6WkaV3C9rSgberAIkW8x9Hf vwiM24ftMs3H3KBCU0N7kL9vhrwwtTPIXxBkR9mXr4ZCbATzkyRwG1wq4BPzUs7TWT6Q/30Jg6FMK kWFewo5A==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vDkpO-0000000H7lH-2Gwj; Tue, 28 Oct 2025 14:37:39 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 6FFB8300220; Tue, 28 Oct 2025 15:37:38 +0100 (CET) Date: Tue, 28 Oct 2025 15:37:38 +0100 From: Peter Zijlstra To: Mel Gorman Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Juri Lelli , Dietmar Eggemann , Valentin Schneider , Chris Mason Subject: Re: [PATCH 1/2] sched/fair: Enable scheduler feature NEXT_BUDDY Message-ID: <20251028143738.GB4067720@noisy.programming.kicks-ass.net> References: <20251027133915.4103633-1-mgorman@techsingularity.net> <20251027133915.4103633-2-mgorman@techsingularity.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251027133915.4103633-2-mgorman@techsingularity.net> On Mon, Oct 27, 2025 at 01:39:14PM +0000, Mel Gorman wrote: > NEXT_BUDDY has been disabled since commit 0ec9fab3d186 ("sched: Improve > latencies and throughput") and LAST_BUDDY was removed in commit 5e963f2bd465 > ("sched/fair: Commit to EEVDF"). The reasoning is not clear but as vruntime > spread is mentioned so the expectation is that NEXT_BUDDY had an impact > on overall fairness. It was not noted why LAST_BUDDY was removed but it > is assumed that it's very difficult to reason what LAST_BUDDY's correct > and effective behaviour should be while still respecting EEVDFs goals. I think I was just struggling to make sense of things and figured less is more and axed it. I have vague memories trying to work through the dynamics of a wakeup-stack and the EEVDF latency requirements and getting a head-ache.