From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: credit2 data structures Date: Thu, 13 Oct 2011 14:54:19 +0200 Message-ID: <4E96DF7B.5060502@ts.fujitsu.com> References: <4E96CEBD020000780005B151@nat28.tlf.novell.com> <4E96F48A020000780005B2A3@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4E96F48A020000780005B2A3@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: George Dunlap , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 10/13/2011 02:24 PM, Jan Beulich wrote: >>>> On 13.10.11 at 12:11, George Dunlap wrote: >> On Thu, Oct 13, 2011 at 10:42 AM, Jan Beulich wrote: >>> Apart from the possibility of allocating the arrays (and maybe also the >>> cpumask_t-s) separately (for which I can come up with a patch on top >>> of what I' currently putting together) - is it really necessary to have >>> all these, the more that there can be multiple instances of the structure >>> with CPU pools? >> I'm not quite sure what it is that you're asking. Do you mean, are >> all of the things in each runqueue structure necessary? Specifically, >> I guess, the cpumask_t structures (because the rest of the structure >> isn't significantly larger than the per-cpu structure for credit1)? > No, it's really the NR_CPUS-sized array of struct csched_runqueue_data. > Credit1 otoh has *no* NR_CPUS sized arrays at all. > >> At first blush, all of those cpu masks are necessary. The assignment >> of cpus to runqueues may be arbitrary, so we need a cpu mask for that. >> In theory, "idle" and "tickled" only need bits for the cpus actually >> assigned to this runqueue (which should be 2-8 under normal >> circumstances). But then we would need some kind of mechanism to >> translate "mask just for these cpus" to "mask of all cpus" in order to >> use the normal cpumask mechanisms, which seems like a lot of extra >> complexity just to save a few bytes. Surely a system with 4096 >> logical cpus can afford 6 megabytes of memory for scheduling? > I'm not concerned about the total amount if run on a system that > large. I'm more concerned about this being a single chunk (possibly > allocated post-boot, where we're really aiming at having no > allocations larger than a page at all) and this size being allocated > even when running on a much smaller system (i.e. depending only > on compile time parameters). > >> For one thing, the number of runqueues in credit2 is actually meant to >> be smaller than the number of logical cpus -- it's meant to be one per >> L2 cache, which should have between 2 and 8 logical cpus, depending on >> the architecture. I just put NR_CPUS because it was easier to get >> working. Making that an array of pointers, which is allocated on an >> as-needed basis, should reduce that requirement a great deal. > That would help, but would probably not suffice (since a NR_CPUS > sized array of pointers is still going to be larger than a page). We > may need to introduce dynamic per-CPU data allocation for this... Couldn't the run-queue data be dynamically allocated and the pcpu-data of credit2 contain a pointer to it? Juergen -- Juergen Gross Principal Developer Operating Systems PDG ES&S SWE OS6 Telephone: +49 (0) 89 3222 2967 Fujitsu Technology Solutions e-mail: juergen.gross@ts.fujitsu.com Domagkstr. 28 Internet: ts.fujitsu.com D-80807 Muenchen Company details: ts.fujitsu.com/imprint.html