From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keith Busch Subject: Re: [PATCH 4/7] node: Add memory caching attributes Date: Mon, 26 Nov 2018 12:53:53 -0700 Message-ID: <20181126195352.GS26707@localhost.localdomain> References: <20181114224921.12123-2-keith.busch@intel.com> <20181114224921.12123-5-keith.busch@intel.com> <20181126190619.GA32595@kroah.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20181126190619.GA32595@kroah.com> Sender: linux-kernel-owner@vger.kernel.org To: Greg Kroah-Hartman Cc: "linux-kernel@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "linux-mm@kvack.org" , Rafael Wysocki , "Hansen, Dave" , "Williams, Dan J" List-Id: linux-acpi@vger.kernel.org On Mon, Nov 26, 2018 at 11:06:19AM -0800, Greg Kroah-Hartman wrote: > On Wed, Nov 14, 2018 at 03:49:17PM -0700, Keith Busch wrote: > > System memory may have side caches to help improve access speed. While > > the system provided cache is transparent to the software accessing > > these memory ranges, applications can optimize their own access based > > on cache attributes. > > > > In preparation for such systems, provide a new API for the kernel to > > register these memory side caches under the memory node that provides it. > > > > The kernel's sysfs representation is modeled from the cpu cacheinfo > > attributes, as seen from /sys/devices/system/cpu/cpuX/cache/. Unlike CPU > > cacheinfo, though, a higher node's memory cache level is nearer to the > > CPU, while lower levels are closer to the backing memory. Also unlike > > CPU cache, the system handles flushing any dirty cached memory to the > > last level the memory on a power failure if the range is persistent. > > > > The exported attributes are the cache size, the line size, associativity, > > and write back policy. > > > > Signed-off-by: Keith Busch > > --- > > drivers/base/node.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++++++ > > include/linux/node.h | 23 ++++++++++ > > 2 files changed, 140 insertions(+) > > > > diff --git a/drivers/base/node.c b/drivers/base/node.c > > index 232535761998..bb94f1d18115 100644 > > --- a/drivers/base/node.c > > +++ b/drivers/base/node.c > > @@ -60,6 +60,12 @@ static DEVICE_ATTR(cpumap, S_IRUGO, node_read_cpumask, NULL); > > static DEVICE_ATTR(cpulist, S_IRUGO, node_read_cpulist, NULL); > > > > #ifdef CONFIG_HMEM > > +struct node_cache_obj { > > + struct kobject kobj; > > + struct list_head node; > > + struct node_cache_attrs cache_attrs; > > +}; > > I know you all are off in the weeds designing some new crazy api for > this instead of this current proposal (sorry, I lost the thread, I'll > wait for the patches before commenting on it), but I do want to say one > thing here. > > NEVER use a raw kobject as a child for a 'struct device' unless you > REALLY REALLY REALLY REALLY know what you are doing and have a VERY good > reason to do so. > > Just use a 'struct device', otherwise you end up having to reinvent all > of the core logic that struct device provides you, like attribute > callbacks (which you had to create), and other good stuff like telling > userspace that a device has shown up so it knows to look at it. > > That last one is key, a kobject is suddenly a "black hole" in sysfs as > far as userspace knows because it does not see them for the most part > (unless you are mucking around in the filesystem on your own, and > really, don't do that, use a library like the rest of the world unless > you really like reinventing everything, which, from your patchset it > feels like...) > > Anyway, use 'struct device'. That's all. > > greg k-h Okay, thank you for the advice. I prefer to reuse over reinvent. :) I only used kobject because the power/ directory was automatically created with 'struct device', but I now I see there are better ways to suppress that.