From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 527F71FFC55 for ; Mon, 17 Mar 2025 22:25:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742250354; cv=none; b=q+xRnNmfx7DBfRbt+IMGZ3sq0VDg7mjV0GbRNzEqiGYsIyTi/6EA6MtVS3ORjatGNuIrscELwvobYe/tNM25kT/osjOj30OmFYkcNR9lQcFDSxTUCrjGRpfCWYpgLuRLiv7+rSSoO8ENPMIvAS/OlwAkkfhEnFIDY1TGfuY/b64= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742250354; c=relaxed/simple; bh=YXhqoFceAYxum5yQk11C06WJaX6rsjvA+greKgjyzeE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JkrPEJyZ1vZ2NVyz+qLnWVfH5m+vSZvfUXKzaQ11yA0CMr4ewvMa96DrjwzIQc5fpI/QNPzBxKtgcixUAJy8LCqQmmphCbM8tebhS0Ay0Zij+ZnrvY8M9r2oR/3lvlfnHtUyP7MIRj/P+Sask8fVNsR7rToEN3NUg+/xgt77sgg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Glubxaow; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Glubxaow" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A0C67C4CEE3; Mon, 17 Mar 2025 22:25:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1742250352; bh=YXhqoFceAYxum5yQk11C06WJaX6rsjvA+greKgjyzeE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GlubxaowKYL7naaoDrfXDA1Z6tgWrFFzyP84pDDyTxVGXuhNbYcM26nViEooAQhQ5 RWzWpCPt6ANnp7+BhUS2pZb2PhewE7zXSeNivONAS11KWCC7mtLQsBzjSoQJSlM9o5 emod+iiF3soWsAQOi5R6nVmRz+3wvBf90JmUGuMoPnLBCbLpLbmkfmtzqpoFtDeMHF X0xMdYBjCt8JF5ak/rAA8WUwBB4iiafMYxveJWCROJWpvXFOx0KZ0mnoCBwcBSFQCi GT9BIJF1EVae6s7/Jbq8UyrtkS0BBeE05iO0OdlbQ0cY3DIv0SPuijuK3qRIoExeD9 MAESUyjMTKGag== Date: Mon, 17 Mar 2025 12:25:50 -1000 From: Tejun Heo To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, David Vernet , Andrea Righi , Changwoo Min , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider Subject: Re: [PATCH RFC] sched_ext: Choose prev_cpu if idle and cache affine without WF_SYNC Message-ID: References: <20250317082803.3071809-1-joelagnelf@nvidia.com> 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: Hello, On Mon, Mar 17, 2025 at 11:07:36PM +0100, Joel Fernandes wrote: ... > > I think it's preferring idle core a > > bit too much - it probably doesn't make sense to cross the NUMA boundary if > > there is an idle CPU in this node, at least. > > Yes, that is a bit extreme. I believe that is what my patch is fixing. If > previous CPU and current CPU share cache, we prefer busy cores with free > previous idle SMT, otherwise go looking for fully idle cores. But it sounds like > from Peter's reply that is not necessarily a good thing to do in case 'fast > numa'. So I guess there is no good answer (?) or way of doing it. Yeah, recent AMD CPUs can be configured into NUMA mode where each chiplet is reported as a node and they do behave like one as each has its own memory connection but the distances among them are significantly closer than traditional multi-socket. That said, I think the implementation is still a bit too happy to jump the boundary. What Andrea is suggesting seems reasonable? Thanks. -- tejun