From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: Load increase after memory upgrade (part2) Date: Tue, 29 Nov 2011 10:33:06 -0500 Message-ID: <20111129153306.GA30908@phenom.dumpdata.com> References: <20111128152829.GC9655@andromeda.dapyr.net> <1322494816.20646.14.camel@zakaz.uk.xensource.com> <20111128164516.GA26664@phenom.dumpdata.com> <1322562199.20646.30.camel@zakaz.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1322562199.20646.30.camel@zakaz.uk.xensource.com> 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 Campbell Cc: Konrad Rzeszutek Wilk , xen-devel , Carsten Schiers , "zhenzhong.duan@oracle.com" , "lersek@redhat.com" List-Id: xen-devel@lists.xenproject.org On Tue, Nov 29, 2011 at 10:23:18AM +0000, Ian Campbell wrote: > On Mon, 2011-11-28 at 16:45 +0000, Konrad Rzeszutek Wilk wrote: > > On Mon, Nov 28, 2011 at 03:40:13PM +0000, Ian Campbell wrote: > > > On Mon, 2011-11-28 at 15:28 +0000, Konrad Rzeszutek Wilk wrote: > > > > On Fri, Nov 25, 2011 at 11:11:55PM +0100, Carsten Schiers wrote: > > > > > > > > I looked through my old mails from you and you explained already the necessity of double > > > > > bounce buffering (PCI->below 4GB->above 4GB). What I don't understand is: why does the > > > > > Xenified kernel not have this kind of issue? > > > > > > > > That is a puzzle. It should not. The code is very much the same - both > > > > use the generic SWIOTLB which has not changed for years. > > > > > > The swiotlb-xen used by classic-xen kernels (which I assume is what > > > Carsten means by "Xenified") isn't exactly the same as the stuff in > > > mainline Linux, it's been heavily refactored for one thing. It's not > > > impossible that mainline is bouncing something it doesn't really need > > > to. > > > > The usage, at least with 'pci_alloc_coherent' is that there is no bouncing > > being done. The alloc_coherent will allocate a nice page, underneath the 4GB > > mark and give it to the driver. The driver can use it as it wishes and there > > is no need to bounce buffer. > > Oh, I didn't realise dma_alloc_coherent was part of swiotlb now. Only a > subset of swiotlb is in use then, all the bouncing stuff _should_ be > idle/unused -- but has that been confirmed? Nope. I hope that the diagnostic patch I have in mind will prove/disprove that. Now I just need to find a moment to write it :-)