From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Theurer Subject: Re: Why is 'emulate' as good as writable PT's? Date: Mon, 05 Jun 2006 17:29:58 -0500 Message-ID: <4484B066.1040201@us.ibm.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ian Pratt Cc: Xen development list , Rolf Neugebauer List-Id: xen-devel@lists.xenproject.org Ian Pratt wrote: >> Could there be situations were we are inadvertently triggering a >> writable page table, where we should just be doing a > update_va_mapping()? > > Almost certainly. Singleton (or small batch) updates should not be using > writeable pagetables, and should use update_va_mapping (or mmu_update if > the VA isn't known or may not be mapped). > > ~18 months ago Rolf wrote and checked in profile code to collect a > histogram of the number of entries found to be modified when writeable > pagetables are flushed. > At the time there was a big spike at '1' which was fixed, but with all > the various linux version upgrades it likely needs revisiting. > > The profile code also records the EIP that caused the writeable > pagetables operation, so if you print out the value a few times you'll > quickly find the culprit. Thanks! It looks like the histogram and EIP logs in ptwr_flush are still there, so we'll run again with perfc=y and see if we can pinpoint the culprit. -Andrew