From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH] x86: enable swiotlb for > 4GiG ram on 32-bit kernels Date: Fri, 19 Oct 2018 07:51:22 +0200 Message-ID: <20181019055122.GA71532@gmail.com> References: <20181014075208.2715-1-hch@lst.de> <20181017163351.GA23719@lst.de> <20181018125116.GA24676@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: whiteheadm-HInyCGIudOg@public.gmane.org Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, Christoph Hellwig , konrad.wilk-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org List-Id: iommu@lists.linux-foundation.org * tedheadster wrote: > > But you said without the fix it doesn't work at all? Or is this > > the same box, just with the aic7xxx controller disabled? > > > > In general the patch should only have two effects: > > > > - set a small amount of memory aside for bounce buffering > > - switch the default dma_ops from dma_direct_ops to swiotlb_ops > > > > I can't really see how either could have such a huge effect, even with > > swiotlb having a couple more wired up ops for which we'd enable spectre > > mitigations. > > > > So a strict before and after would be very interesting, if it is really > > just this one change that causes such a huge drop we have hidden dragons > > somewhere.. > > Christoph, > I did a very controlled before-and-after and got very sensible > results. All compiles were close in time with patched and un-patched > kernels. > > I must have screwed something up with my last round of testing. > > Ingo: I am confident this patch should be accepted. Thanks for the update, I've re-applied this to tip:x86/urgent. Ingo