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 1B64C21322F for ; Wed, 7 May 2025 07:06:09 +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=1746601570; cv=none; b=OOvuOwfdPCCHUmns2qEgAjzu6dOPSQ2n4Zqxa134Gi3xhGECw7Y7LmjrYRHLwyPqwAlPiLF4CB9Q30AqNHt2Y8NKETfnvuiqr7C6XN5sMXWwyFxWIYBBXJPOPB8AQTlDbjbRuXi0ePX/m+Ions4bi+61LMFBzpFi+Gp6gylUjio= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746601570; c=relaxed/simple; bh=FpwjGacwhaY9kZl59YWuCAhiL+olHRZOUpT5HisyEJI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HGBEsdSL00FENx1tmEvxsK6YtPW6V97Uez9guNC7/bomBsWyyEk7sKZxjZhVacWGxrg6RvKxhilDNIjAvH+Uvt969OkUycpBaSIE8vmgm7AmX/cJtT8/zzKyDlhKxKB/ZYsE1nWmdXXxglMyJJkoBOsKhrYVWxrVgl8UVvfjZ90= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ryOHF0Vl; 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="ryOHF0Vl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 73CCEC4CEE7; Wed, 7 May 2025 07:06:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746601569; bh=FpwjGacwhaY9kZl59YWuCAhiL+olHRZOUpT5HisyEJI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ryOHF0VlY+5ct3A928IV4oRJhllRsR+f/AYziw6maq+C58FF/+fAMk851I7ikHgRu wVEYoMNiAPxWD7I6G2nsKEN9XbXJy7EsO4PbaXIM9lVEaN8Kcq0MeNHjZ7Hm7e/TyA rJ0YFVtPtEl1Pfaw28Gvv3649vPwmcGP4Fm7fTKCfUDaZzM6vKLYkQIYBwMLFQBM3g A8sjcGZcUdjJ6+pqH/txhE75nO75pjFJOHaTqP2L5BVtw72tJI8p5yI5Hq8MLujzHu MannzQp7slurCqeHhu+ZAlzVKCoKSzhGUmb/ZydhR9njOpB4cUa7n5jyId3HsB57Eg u0t1zyGP4TyIw== Date: Wed, 7 May 2025 09:06:04 +0200 From: Ingo Molnar To: Yafang Shao , Peter Zijlstra Cc: ardb@kernel.org, arnd@arndb.de, bp@alien8.de, dwmw@amazon.co.uk, hpa@zytor.com, linux-kernel@vger.kernel.org, michal.lkml@markovi.net, peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org, vkuznets@redhat.com, yamada.masahiro@socionext.com Subject: Re: [PATCH 13/15] x86/kconfig/64: Enable popular scheduler, cgroups and namespaces options in the defconfig Message-ID: References: <20250506170924.3513161-14-mingo@kernel.org> <9b31f1df-7dc6-468b-9418-0b13239df8bc@gmail.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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9b31f1df-7dc6-468b-9418-0b13239df8bc@gmail.com> * Yafang Shao wrote: > Hello Mingo, > > > +CONFIG_VIRT_CPU_ACCOUNTING_GEN=y > > +CONFIG_IRQ_TIME_ACCOUNTING=y > > Enabling CONFIG_IRQ_TIME_ACCOUNTING=y can lead to user-visible behavioral > changes. For more context, please refer to the related discussion here: > https://lore.kernel.org/all/20241222024734.63894-1-laoar.shao@gmail.com/ . Yeah. I actually agree with your series. It (re-)includes IRQ/softirq time in task CPU usage statistics even under IRQ_TIME_ACCOUNTING=y, while still keeping the finegrained IRQ/softirq statistics as well, correct? The Kconfig option is also arguably rather misleading: config IRQ_TIME_ACCOUNTING bool "Fine granularity task level IRQ time accounting" depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE help Select this option to enable fine granularity task irq time accounting. This is done by reading a timestamp on each transitions between softirq and hardirq state, so there can be a small performance impact. It only warns about a small performance impact, but doesn't warn that CPU accounting is changed in an incompatible fashion that surprises tooling... But I think we should probably treat this as a bug, not as lack of documentation. Peter, do you concur? > If we decide to enable it by default, we should clearly document this > behavior change. Below is the patch I wrote earlier but haven’t sent > out for review yet. Note that it's not enabled by default - this patch is just about the x86 defconfig. Thanks, Ingo