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 C783C1A9B5A for ; Wed, 20 Nov 2024 14:51:57 +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=1732114319; cv=none; b=LsNsXKgHSlNZQ2A5VysjwRFPHrMOzBaJtRIF/uMWyxNYzcOz9tAK/jHP3iWQlObFrHcdXVtJdEZ49LGcnd2s617180o5qUntqawKJvGh0mcrw/RT+7SuODKi9Ln8DAwRIvbgUiHHQjK6IieK0cVJDaBDoli3bg6lzY+rGEIHXzU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732114319; c=relaxed/simple; bh=4gJefIEkFg4zHIzKYkMPiQJS/Kz94ehYi8VfErbkJYo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=lRhFrbytfzz5hrfWh4IFkTju1dLw+Q/7HZZfzYTHhHAzVZjqgyXVKGcJIcEILtsiid3UBfdKQRqVBtky7ux6zjEjkcoY+WyI0d1quTA4SQZgpnmOXHoE9SGLz9KiXDFpOZwiFX3mbhmWb7+fOYifhn2VuQcJBMncN2tK3xjh6Y0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (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=wZK/fjZe; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (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="wZK/fjZe" 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=Tw/QhYWKrpU75sqxyl3mlwNFxdhKMu7qoH9/t8NsVhc=; b=wZK/fjZeS6+u9pVldcySVZFZMl +tccmauTQkw9wtI/E1FF09hgVNDeXC1RX8BI9qYZVDczXnX5DW22CFvOqon2z+stKt9IdiOrAefgE 8hhH8bcmopGcCRtzo5Yje+DQ9NbfLZybfVPq9JczE/Z9jK5aDsDUscHvtrjFMCgZV4XoWdffPVW17 ZJwbkSMcrnx91w2KKsm5cWyM4/WQtcghRZsF75XLRSvV4+p1PmGoMW+1UApQ/J14NHdvOYV6TmlBA fvMrKwiPyI1ydIIPkF6x3soeR+mpfLmuArsakav6VZn66jgHeFSS3zQmbkeR5Vd+6o77//chFqtc3 gQ/ZSF/w==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tDm2a-00000005MZH-1QrJ; Wed, 20 Nov 2024 14:50:49 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 345E030023F; Wed, 20 Nov 2024 15:50:49 +0100 (CET) Date: Wed, 20 Nov 2024 15:50:49 +0100 From: Peter Zijlstra To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, x86@kernel.org, rcu@vger.kernel.org, linux-kselftest@vger.kernel.org, "Paul E . McKenney" , Steven Rostedt , Masami Hiramatsu , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Andy Lutomirski , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Josh Poimboeuf , Jason Baron , Kees Cook , Sami Tolvanen , Ard Biesheuvel , Nicholas Piggin , Juerg Haefliger , Nicolas Saenz Julienne , "Kirill A. Shutemov" , Nadav Amit , Dan Carpenter , Chuang Wang , Yang Jihong , Petr Mladek , "Jason A. Donenfeld" , Song Liu , Julian Pidancet , Tom Lendacky , Dionna Glaze , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Juri Lelli , Marcelo Tosatti , Yair Podemsky , Daniel Wagner , Petr Tesarik Subject: Re: [RFC PATCH v3 04/15] rcu: Add a small-width RCU watching counter debug option Message-ID: <20241120145049.GI19989@noisy.programming.kicks-ass.net> References: <20241119153502.41361-1-vschneid@redhat.com> <20241119153502.41361-5-vschneid@redhat.com> Precedence: bulk X-Mailing-List: bpf@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: <20241119153502.41361-5-vschneid@redhat.com> On Tue, Nov 19, 2024 at 04:34:51PM +0100, Valentin Schneider wrote: > A later commit will reduce the size of the RCU watching counter to free up > some bits for another purpose. Paul suggested adding a config option to > test the extreme case where the counter is reduced to its minimum usable > width for rcutorture to poke at, so do that. > > Make it only configurable under RCU_EXPERT. While at it, add a comment to > explain the layout of context_tracking->state. Note that this means it will get selected by allyesconfig and the like, is that desired? If no, depends on !COMPILE_TEST can help here.