From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753004AbYIBOgT (ORCPT ); Tue, 2 Sep 2008 10:36:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751387AbYIBOgH (ORCPT ); Tue, 2 Sep 2008 10:36:07 -0400 Received: from smtp03.osg.ufl.edu ([128.227.74.70]:43236 "EHLO smtp.ufl.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751351AbYIBOgG (ORCPT ); Tue, 2 Sep 2008 10:36:06 -0400 Message-ID: <1147742858.207301220366162943.JavaMail.osg@osgjas01.cns.ufl.edu> Date: Tue, 2 Sep 2008 10:36:02 -0400 (EDT) From: "CHADHA,VINEET" To: Nick Piggin , "CHADHA,VINEET" Subject: Re: TLB evaluation for Linux Cc: linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: GatorMail WebMail (http://GatorMail.sf.net/) X-Originating-IP: 10.5.153.246 [10.5.153.246] X-UFL-Spam-Status: hits=-2.5, required=5, tests=ALL_TRUSTED,TW_VL X-UFL-Scanned-By: CNS Open Systems Group (http://open-systems.ufl.edu/services/smtp-relay/) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks Nick. A PhD dissertation to study scalability of micro-kernels can be found : http://l4ka.org/publications/2005/uhlig_phd-thesis_scalability.pdf An example of study I would like to do through Full system simulator is in Figure 4.11. Regarding TLB flushing modifications, I will get back to you (and mailing list) after I get a better understanding of source code. Regards, Vineet On Tue Sep 02 00:39:00 EDT 2008, Nick Piggin wrote: > On Tuesday 02 September 2008 14:12, CHADHA,VINEET wrote: >> Hi, >> >> I have been working to evaluate TLB performance for Linux O/S and >> virtualized workloads(such as Xen) in a Full system >> simulator(e.g. >> simics). While my evaluation is in nascent stage, I do notice >> that >> most of the IPIs in multi-core environments cause complete TLB >> Flush. >> >> I want to evaluate cost of TLB shootdown including re-population >> vs. each entry shootdown (invlpg). While a similar study has been >> done in other kernels (e.g. L4 kernel), I am not aware if it has >> been done for Linux O/S. > > This is a very interesting area to investigate. Do you have a > link to > any of the existing studies? > > >> Are there hooks or patches to test or evaluate TLB performance. >> Specifically, I would like to know where to make changes in Linux >> kernel to support each entry shootdown. > > The main thing I guess is to look at tlb_flush(), called by > tlb_flush_mmu > when unmapping user virtual memory, which on x86 is going to call > flush_tlb_mm, which flushes the entire tlb. > > It would need a bit of reworking of things in order to store the > virtual > address corresponding to each page in the struct mmu_gather, and > then > deciding to branch off to do multiple invlpg if you have only a > small > number of pages to be flushed. I'd suggest the easiest way to get > something working on x86 would be to modify the asm-generic > infrastructure > (ignore other architectures for the time being). > > You will also have to rework the IPI flushing scheme so that it > can handle > more than one flush_va for invlpg invalidations. > > After you get all this done, you could also look at applying > similar > heuristics to flush_tlb_range. This one should be much easier at > this point, > but it is used in fewer places (eg. mprotect). > >