From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Holt Date: Wed, 17 Mar 2004 12:27:15 +0000 Subject: Re: pgd_free, pmd_free, and pte_free trapping memory. Message-Id: <20040317122714.GD2119@lnx-holt> List-Id: References: <20040316112424.GA20203@lnx-holt> In-Reply-To: <20040316112424.GA20203@lnx-holt> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Tue, Mar 16, 2004 at 10:06:18PM -0800, David Mosberger wrote: > >>>>> On Tue, 16 Mar 2004 09:24:55 -0600, Robin Holt said: > > Robin> I have a kernel with these ripped out. I have run one simple > Robin> Aim7 run on a 32P system. The performance fell in the noise > Robin> range of a normal Aim7 run. Is this a good test to run? > Robin> Should I focus on any specific benchmark, or run a suite? > > For this kind of test, I'd rather see a micro-benchmark to establish > the worst-case effect. Then we have an upper bound and can make a > judgment as to whether or not that's a likely scenario. And yes, this > would mean that you'd probably want to measure it on a relative small > system (certainly not NUMA, perhaps just UP). I am currently looking into Christoph's suggestion of using a per cpu page allocator. Unfortunately, yesterday was a little busy and I didn't get much of a chance to look into it. > > >> That's less code and thus less complexity which is always good. > >> Now if the pre-zeroing actually makes a difference we might have > >> to keep small pre-zeroed list around, but I doubt this is really > >> good idea (or even nessecary) > > Robin> The page zeroing costs 4uSec per page (I believe that is the > Robin> number). With a typical fork taking approx 40 pages, that > Robin> should be felt during an Aim7 run. It looks like caches are > Robin> masking some of that out. > > Try UP. Also, what if the page-size is 64KB? In any case, 4usec is a > lot. I got the 4uSec from Jack Steiner. I don't know if he tested it with 64KB pages. I will check.