From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ralph Campbell Subject: Re: [openib-general] [PATCH 39 of 39] IB/ipath - use streaming copy in RDMA interrupt handler to reduce packet loss Date: Thu, 29 Jun 2006 16:55:41 -0700 Message-ID: <1151625341.4572.133.camel@brick.pathscale.com> References: <1151618377.10886.23.camel@chalcedony.pathscale.com> <20060629.150319.104035601.davem@davemloft.net> <1151624063.10886.34.camel@chalcedony.pathscale.com> <20060629.164623.59469884.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: bos@pathscale.com, akpm@osdl.org, netdev@vger.kernel.org, rdreier@cisco.com, linux-kernel@vger.kernel.org, openib-general@openib.org Return-path: Received: from mx.pathscale.com ([64.160.42.68]:45979 "EHLO mx.pathscale.com") by vger.kernel.org with ESMTP id S1751318AbWF2Xzn (ORCPT ); Thu, 29 Jun 2006 19:55:43 -0400 To: David Miller In-Reply-To: <20060629.164623.59469884.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org This is intended to be an architecture specific function so if the CPU does support HW dma to the CPU's L2 cache, the architecture specific version of memcpy_nc() would not replace the default definition which maps memcpy_nc() to memcpy(). For CPUs like the vast majority currently available, there is a performance benefit by not reading data into the cache that won't be read a second time. On Thu, 2006-06-29 at 16:46 -0700, David Miller wrote: > From: Bryan O'Sullivan > Date: Thu, 29 Jun 2006 16:34:23 -0700 > > > I'm not quite following you, though I assume you're referring to Niagara > > or Rock :-) Are you saying a memcpy_nc would do worse than plain > > memcpy, or worse than some other memcpy-like routine? > > It would do worse than memcpy. > > If you bypass the L2 cache, it's pointless because the next > agent (PCI controller, CPU thread, etc.) is going to need the > data in the L2 cache. > > It's better in that kind of setup to eat the L2 cache miss overhead in > memcpy since memcpy can usually prefetch and store buffer in order to > absorb some of the L2 miss costs. > > _______________________________________________ > openib-general mailing list > openib-general@openib.org > http://openib.org/mailman/listinfo/openib-general > > To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general >