From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K.V" Subject: Re: [PATCH V2] powerpc/infiniband: Use cache inhibitted and guarded mapping on powerpc Date: Sun, 24 Apr 2016 23:03:10 +0530 Message-ID: <87shyanc89.fsf@skywalker.in.ibm.com> References: <1461139097-10213-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1461278876.3135.18.camel@kernel.crashing.org> <20160422160927.GB12897@obsidianresearch.com> <1461399949.3135.52.camel@kernel.crashing.org> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <1461399949.3135.52.camel-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Benjamin Herrenschmidt , Jason Gunthorpe Cc: paulus-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org, mpe-Gsx/Oe8HsFggBc27wqDAHg@public.gmane.org, linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, Mike Marciniszyn , Doug Ledford , Sean Hefty , Hal Rosenstock , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-rdma@vger.kernel.org Benjamin Herrenschmidt writes: > On Fri, 2016-04-22 at 10:09 -0600, Jason Gunthorpe wrote: >> On Fri, Apr 22, 2016 at 08:47:56AM +1000, Benjamin Herrenschmidt >> wrote: >> > >> > On Wed, 2016-04-20 at 03:58 -0400, Aneesh Kumar K.V wrote: >> > > >> > > The driver was requesting for a writethrough mapping. But with >> > > thoses >> > > flags we will end up with a SAO mapping because we now have >> > > memory >> > > conherence always enabled. ie, the existing mapping will end up >> > > with >> > > a WIMG value 0b1110 which is Strong Access Order. >> > > >> > > Update this to use cache inhibitted guarded mapping >> > Why guarded ? If it's performance sensitive (and the driver has >> > appropriate barriers where needed), you will get write combining >> > without guarded, you won't with it. >> This driver uses uncached write combining on x86 > > Right so if you want something similar on power, use the _wc variant, > and make sure you have the appropriate barriers when you need to > break combining. > > Cheers, > Ben. The code after change looks like below #if defined(__powerpc__) vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); #endif /* * don't allow them to later change to readable with mprotect (for when * not initially mapped readable, as is normally the case) */ vma->vm_flags &= ~VM_MAYREAD; vma->vm_flags |= VM_DONTCOPY | VM_DONTEXPAND; /* We used PAT if wc_cookie == 0 */ if (!dd->wc_cookie) vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot); So it uses pgprot_noncached_wc if (!dd->wc_cookie). Hence I was thinking it needs more stricter mapping otherwise. -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html