From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id E3FD029A33E; Wed, 27 Aug 2025 10:51:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756291867; cv=none; b=LSAeUifq4Yr/Rebpbam/k07SuLjxpzCX+1/EHZHN3uEBCWDo1/Jb5syiyACYT8ONad4Ats71scheI4udB9udKDvSqo3b+a75qIZRUcKk9Y11dRERDm7ywXwlIFyCsSC6IFRHGMPgVifA1kSpQjxRT6aKZJCMmRhymFM/e+Khihk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756291867; c=relaxed/simple; bh=xGhFfyWh4KX+AimhvcHJiy92QfbQuckwtomVxT/PI7g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=L19H43lHl0iOKFXd3nc88+KEAAKBIl29zofXzMkh0lS6goQ4wBV8xmiQYTU75JouO6J3DwJgam9DB8MrZcJwknsPb4kbx64rV0QWhdi/KWcI/PNepRCb1A/kjoMNi89e1/PfPD9ZgN2GOfVk2FooARWEgcjbMDabxUxzBWINP1g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DC9951688; Wed, 27 Aug 2025 03:50:56 -0700 (PDT) Received: from e133380.arm.com (e133380.arm.com [10.1.197.68]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 646113F738; Wed, 27 Aug 2025 03:50:59 -0700 (PDT) Date: Wed, 27 Aug 2025 11:50:56 +0100 From: Dave Martin To: James Morse Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org, devicetree@vger.kernel.org, shameerali.kolothum.thodi@huawei.com, D Scott Phillips OS , carl@os.amperecomputing.com, lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com, baolin.wang@linux.alibaba.com, Jamie Iles , Xin Hao , peternewman@google.com, dfustini@baylibre.com, amitsinght@marvell.com, David Hildenbrand , Rex Nie , Koba Ko , Shanker Donthineni , fenghuay@nvidia.com, baisheng.gao@unisoc.com, Jonathan Cameron , Rob Herring , Rohit Mathew , Rafael Wysocki , Len Brown , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Krzysztof Kozlowski , Conor Dooley , Catalin Marinas , Will Deacon , Greg Kroah-Hartman , Danilo Krummrich Subject: Re: [PATCH 05/33] ACPI / PPTT: Find cache level by cache-id Message-ID: References: <20250822153048.2287-1-james.morse@arm.com> <20250822153048.2287-6-james.morse@arm.com> Precedence: bulk X-Mailing-List: linux-acpi@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: <20250822153048.2287-6-james.morse@arm.com> Hi, On Fri, Aug 22, 2025 at 03:29:46PM +0000, James Morse wrote: > The MPAM table identifies caches by id. The MPAM driver also wants to know > the cache level to determine if the platform is of the shape that can be > managed via resctrl. Cacheinfo has this information, but only for CPUs that > are online. > > Waiting for all CPUs to come online is a problem for platforms where > CPUs are brought online late by user-space. > > Add a helper that walks every possible cache, until it finds the one > identified by cache-id, then return the level. > Add a cleanup based free-ing mechanism for acpi_get_table(). Does this mean that the early secondaries must be spread out across the whole topology so that everything can be probed? (i.e., a random subset is no good?) If so, is this documented somewhere, such as in booting.rst? Maybe this is not a new requirement -- it's not an area that I'm very familiar with. > > CC: Jonathan Cameron > Signed-off-by: James Morse > --- > Changes since RFC: > * acpi_count_levels() now returns a value. > * Converted the table-get stuff to use Jonathan's cleanup helper. > * Dropped Sudeep's Review tag due to the cleanup change. > --- > drivers/acpi/pptt.c | 64 ++++++++++++++++++++++++++++++++++++++++++++ > include/linux/acpi.h | 17 ++++++++++++ > 2 files changed, 81 insertions(+) > > diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c > index 8f9b9508acba..660457644a5b 100644 > --- a/drivers/acpi/pptt.c > +++ b/drivers/acpi/pptt.c > @@ -907,3 +907,67 @@ int find_acpi_cpu_topology_hetero_id(unsigned int cpu) > return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE, > ACPI_PPTT_ACPI_IDENTICAL); > } > + > +/** > + * find_acpi_cache_level_from_id() - Get the level of the specified cache > + * @cache_id: The id field of the unified cache > + * > + * Determine the level relative to any CPU for the unified cache identified by > + * cache_id. This allows the property to be found even if the CPUs are offline. > + * > + * The returned level can be used to group unified caches that are peers. > + * > + * The PPTT table must be rev 3 or later, > + * > + * If one CPUs L2 is shared with another as L3, this function will return > + * an unpredictable value. > + * > + * Return: -ENOENT if the PPTT doesn't exist, or the cache cannot be found. Nit: doesn't exist or its revision is too old. > + * Otherwise returns a value which represents the level of the specified cache. > + */ > +int find_acpi_cache_level_from_id(u32 cache_id) > +{ > + u32 acpi_cpu_id; > + int level, cpu, num_levels; > + struct acpi_pptt_cache *cache; > + struct acpi_pptt_cache_v1 *cache_v1; > + struct acpi_pptt_processor *cpu_node; > + struct acpi_table_header *table __free(acpi_table) = acpi_get_table_ret(ACPI_SIG_PPTT, 0); acpi_get_pptt() ? (See comment on patch 3.) Comments there also suggest that the acpi_put_table() may be unnecessary, at least on some paths. I haven't tried to understand the ins and outs of this. > + > + if (IS_ERR(table)) > + return PTR_ERR(table); > + > + if (table->revision < 3) > + return -ENOENT; > + > + /* > + * If we found the cache first, we'd still need to walk from each CPU > + * to find the level... > + */ ^ Possibly confusing comment? The cache id is the starting point for calling this function. Is there a world in which we are at this point without first having found the cache node? (If the comment is just a restatement of part of the kerneldoc description, maybe just drop it.) > + for_each_possible_cpu(cpu) { > + acpi_cpu_id = get_acpi_id_for_cpu(cpu); > + cpu_node = acpi_find_processor_node(table, acpi_cpu_id); > + if (!cpu_node) > + return -ENOENT; > + num_levels = acpi_count_levels(table, cpu_node, NULL); Is the initial call to acpi_count_levels() really needed here? It feels a bit like we end up enumerating the whole topology two or three times here; once to count how many levels there are, and then again to examine the nodes, and once more inside acpi_find_cache_node(). Why can't we just walk until we run out of levels? I may be missing some details of how these functions interact -- if this is only run at probe time, compact, well-factored code is more important than making things as fast as possible. > + > + /* Start at 1 for L1 */ > + for (level = 1; level <= num_levels; level++) { > + cache = acpi_find_cache_node(table, acpi_cpu_id, > + ACPI_PPTT_CACHE_TYPE_UNIFIED, > + level, &cpu_node); > + if (!cache) > + continue; > + > + cache_v1 = ACPI_ADD_PTR(struct acpi_pptt_cache_v1, > + cache, > + sizeof(struct acpi_pptt_cache)); > + > + if (cache->flags & ACPI_PPTT_CACHE_ID_VALID && > + cache_v1->cache_id == cache_id) > + return level; > + } > + } > + > + return -ENOENT; > +} > diff --git a/include/linux/acpi.h b/include/linux/acpi.h > index f97a9ff678cc..30c10b1dcdb2 100644 > --- a/include/linux/acpi.h > +++ b/include/linux/acpi.h [...] > @@ -221,6 +222,17 @@ void acpi_reserve_initial_tables (void); > void acpi_table_init_complete (void); > int acpi_table_init (void); > > +static inline struct acpi_table_header *acpi_get_table_ret(char *signature, u32 instance) > +{ > + struct acpi_table_header *table; > + int status = acpi_get_table(signature, instance, &table); > + > + if (ACPI_FAILURE(status)) > + return ERR_PTR(-ENOENT); > + return table; > +} This feels like something that ought to exist already. If not, why not? If so, are there open-coded versions of this spread around the ACPI tree that should be ported to use it? [...] Cheers ---Dave