From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 03/10] x86: add initialization code for DMA-API debugging Date: Fri, 21 Nov 2008 18:19:52 +0100 Message-ID: <20081121171952.GL733@elte.hu> References: <1227284770-19215-1-git-send-email-joerg.roedel@amd.com> <1227284770-19215-4-git-send-email-joerg.roedel@amd.com> <20081121165628.GD733@elte.hu> <20081121171004.GE1386@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ingo Molnar , Thomas Gleixner , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, iommu@lists.linux-foundation.org To: Joerg Roedel Return-path: Received: from mx3.mail.elte.hu ([157.181.1.138]:49781 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753858AbYKURUo (ORCPT ); Fri, 21 Nov 2008 12:20:44 -0500 Content-Disposition: inline In-Reply-To: <20081121171004.GE1386@amd.com> Sender: netdev-owner@vger.kernel.org List-ID: * Joerg Roedel wrote: > On Fri, Nov 21, 2008 at 05:56:28PM +0100, Ingo Molnar wrote: > > > + return (entry->dev_addr >> HASH_FN_SHIFT) & HASH_FN_MASK; > > > +} > > > + > > > +static struct dma_debug_entry *dma_entry_alloc(void) > > > +{ > > > + gfp_t gfp = GFP_KERNEL | __GFP_ZERO; > > > + > > > + if (in_atomic()) > > > + gfp |= GFP_ATOMIC; > > > + > > > + return kmem_cache_alloc(dma_entry_cache, gfp); > > > > hm. that slab allocation in the middle of DMA mapping ops makes me a > > bit nervous. the DMA mapping ops are generally rather atomic. > > > > and in_atomic() check there is a bug on !PREEMPT kernels, so it wont > > fly. > > I am not sure I understand this correctly. You say the check for > in_atomic() will break on !PREEMPT kernels? Correct. There is no check to be able to tell whether we can schedule or not. I.e. on !PREEMPT your patches will crash and burn. > > We dont have a gfp flag passed in as all the DMA mapping APIs > > really expect all allocations having been done in advance already. > > Hmm, I can change the code to pre-allocate a certain (configurable?) > number of these entries and disble the checking if we run out of it. yeah, that's a good approach too - that's what lockdep does. Perhaps make the max entries nr a Kconfig entity - so it can be tuned up/down depending on what type of iommu scheme is enabled. Ingo