From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jack Steiner Date: Wed, 28 Aug 2002 19:55:05 +0000 Subject: Re: [Linux-ia64] [RFD] physical memory granularity Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org > > Linux on IA64 currently supports "granules" of 16MB and 64MB. > This is the page size used for the kernel identity-mapped > regions. Everything mapped by a page must actually exist (to > avoid MCAs when prefetching into a hole) and must have the same > attributes (to avoid attribute aliasing), so we assume that > physical memory comes in granule-sized chunks. > > DIG64 2.1 says nothing about the granularity of physical memory, > but it seems that for all existing IA64 machines, memory comes in > chunks of at least 64MB. But there's an HP machine in the pipe > that may support only 4MB granularity. > > I'm not keen on reducing the granule size to 4MB, because I'm > afraid the extra TLB misses will be a noticeable performance > problem. Does anybody have any quantitative data on the effect > of granule size on performance? Certainly nothing conclusive, but .... About 6 months ago, I ran the AIM7 benchmark with 16MB & 64MB granules. No measurable difference. The runs were indistinguishable. However, with other benchmarks (or 4MB granules), YMMV. > Or any strong opinions on what > granule sizes we should support? > > Bjorn > > _______________________________________________ > Linux-IA64 mailing list > Linux-IA64@linuxia64.org > http://lists.linuxia64.org/lists/listinfo/linux-ia64 > -- Thanks Jack Steiner (651-683-5302) (vnet 233-5302) steiner@sgi.com