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 84F27170A01; Fri, 22 Nov 2024 20:08:07 +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=1732306087; cv=none; b=snQG4hFEnf/5YAssifXxEr2l7vvpmf01ew+MHWm/j6iWnuh9gCT1wPa9wQCAeAlvZFmuOKX53nrrKwDkOfUYBeUgPL2ZA1jzUN0ujhXWdo9Bixxu9SW3bU64Ev38UX0MOGsS3evwWRrEV1+mRjWzh2gPZwg1DVkZqmdnvlEQnmk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732306087; c=relaxed/simple; bh=H0WGmc4fhp39hrLk/vQe7lwz9wX1lQ6E3eONcDXE/oA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=A9NCzTSSh7IykUD+w6XvpBsmLMD93CBttv418Gqbp6J9kediD+ifSyl9J4Wfc+4Nt2TV5KFketuJCALw76oPHNcagyACoXm4V+nMGF6syZliZ6f58q1S2ut5EsJiZOAv7N4HlZ5ROvqJv/fWV6KLkVJPjxOCVUVMBJjmFtdN1RU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rlYmRLNc; 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="rlYmRLNc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E9AD5C4CECE; Fri, 22 Nov 2024 20:08:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732306087; bh=H0WGmc4fhp39hrLk/vQe7lwz9wX1lQ6E3eONcDXE/oA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rlYmRLNcffA8BvAM4uw6etJfi/PZzuVciDoR8K2G4yoTG/5mD3yMLjxsgG3TGWANb 3doU9hmKBXdKwDtm8VOPPY3ZSrU1Idx+Cb4qnY4RnHZFRYc0mCS5zJnt2EUZVdkYpk 9LYkwAB6pQqx5JJLgxu8Q/0ImqAUtmjZi4/P1ZOKMgCCk+oqzrgvWTc6I2N++Q0P3q UujM2u8gxY4fSw0r+LLgdXJIs1+3Q58aTxXI5uJV/aNA5GV9ZLbxZ4hqIUz4bcipFG 4j1d/2tl6uOhhVUFP3q6zy+2Njw9ORvRCLNvMqRcoTeECfobtjuu/vo+a1365PtVpY NlffSSWBsg9TA== From: SeongJae Park To: Jonathan Cameron Cc: SeongJae Park , Gregory Price , linux-cxl@vger.kernel.org, linux-mm@kvack.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, tongtiangen@huawei.com, Yicong Yang , Niyas Sait , ajayjoshi@micron.com, Vandana Salve , Davidlohr Bueso , Dave Jiang , Alison Schofield , Ira Weiny , Dan Williams , Alexander Shishkin , Peter Zijlstra , Ingo Molnar , "Arnaldo Carvalho de Melo" , Mark Rutland , Huang Ying Subject: Re: [RFC PATCH 0/4] CXL Hotness Monitoring Unit perf driver Date: Fri, 22 Nov 2024 12:08:03 -0800 Message-Id: <20241122200803.59369-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20241121145852.00000460@huawei.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Thu, 21 Nov 2024 14:58:52 +0000 Jonathan Cameron wrote: > On Thu, 21 Nov 2024 09:24:43 -0500 > Gregory Price wrote: > > > On Thu, Nov 21, 2024 at 10:18:41AM +0000, Jonathan Cameron wrote: [...] > Just working out how to tune the hardware to grab useful data is going > to take a while to figure out, let alone doing anything much with it. > > Without care you won't get a meaningful signal for what is actually > hot out of the box. Lots of reasons why including: > a) Exhaustion of tracking resources, due to looking at too large a window > or for too long. Will probably need some form of auto updating of > what is being scanning (coarse to fine might work though I'm doubtful, > scanning across small regions maybe). > b) Threshold too high, no detections. > c) Threshold too low, everything hot. > d) Wrong timescales. Hot is not a well defined thing. > e) Hardware that won't do tracking at fine enough granularity. Similar questions can be raised to general hotness monitoring including that for DAMON. I'm trying to summarize[1] rules of thumbs for DAMON tuning based on my humble experiences. Once it is done, I will further try automations of tunings. In future, hopefully DAMON can be extended to utilize CXL hotness monitoring unit as low level primitive for access check. Then, the guidance and automation of DAMON tuning could be just applied. Note that I'm not saying DAMON should be the only way to utilize CXL hotness monitoring unit. I'm saying DAMON could be one of the ways :) [1] https://lore.kernel.org/20241108232536.73843-1-sj@kernel.org Thanks, SJ [...]