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Thu, 26 Nov 2020 22:31:13 -0800 Received: from MTKMBS32N1.mediatek.inc (172.27.4.71) by MTKMBS62DR.mediatek.inc (172.29.94.18) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 26 Nov 2020 22:21:08 -0800 Received: from MTKCAS36.mediatek.inc (172.27.4.186) by MTKMBS32N1.mediatek.inc (172.27.4.71) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 27 Nov 2020 14:21:04 +0800 Received: from [10.17.3.153] (10.17.3.153) by MTKCAS36.mediatek.inc (172.27.4.170) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Fri, 27 Nov 2020 14:21:02 +0800 Message-ID: <1606458063.26323.190.camel@mhfsdcap03> Subject: Re: [PATCH] iommu: Improve the performance for direct_mapping From: Yong Wu To: Robin Murphy Date: Fri, 27 Nov 2020 14:21:03 +0800 In-Reply-To: References: <20201120090628.6566-1-yong.wu@mediatek.com> X-Mailer: Evolution 3.10.4-0ubuntu2 MIME-Version: 1.0 X-TM-SNTS-SMTP: 8385ECAE0D6D3223BDD513D2FBE4AE4F466D2488E98D903708BC01BA7A1574042000:8 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201127_013121_274064_72463C8A X-CRM114-Status: GOOD ( 31.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: youlin.pei@mediatek.com, anan.sun@mediatek.com, Nicolas Boichat , srv_heupstream@mediatek.com, Tomasz Figa , Joerg Roedel , linux-kernel@vger.kernel.org, Krzysztof Kozlowski , chao.hao@mediatek.com, iommu@lists.linux-foundation.org, linux-mediatek@lists.infradead.org, Matthias Brugger , Will Deacon , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 2020-11-26 at 15:19 +0000, Robin Murphy wrote: > On 2020-11-20 09:06, Yong Wu wrote: > > Currently direct_mapping always use the smallest pgsize which is SZ_4K > > normally to mapping. This is unnecessary. we could gather the size, and > > call iommu_map then, iommu_map could decide how to map better with the > > just right pgsize. > > > > From the original comment, we should take care overlap, otherwise, > > iommu_map may return -EEXIST. In this overlap case, we should map the > > previous region before overlap firstly. then map the left part. > > > > Each a iommu device will call this direct_mapping when its iommu > > initialize, This patch is effective to improve the boot/initialization > > time especially while it only needs level 1 mapping. > > > > Signed-off-by: Anan Sun > > Signed-off-by: Yong Wu > > --- > > drivers/iommu/iommu.c | 20 ++++++++++++++++++-- > > 1 file changed, 18 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > > index df87c8e825f7..854a8fcb928d 100644 > > --- a/drivers/iommu/iommu.c > > +++ b/drivers/iommu/iommu.c > > @@ -737,6 +737,7 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group, > > /* We need to consider overlapping regions for different devices */ > > list_for_each_entry(entry, &mappings, list) { > > dma_addr_t start, end, addr; > > + size_t unmapped_sz = 0; > > > > if (domain->ops->apply_resv_region) > > domain->ops->apply_resv_region(dev, domain, entry); > > @@ -752,10 +753,25 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group, > > phys_addr_t phys_addr; > > > > phys_addr = iommu_iova_to_phys(domain, addr); > > - if (phys_addr) > > + if (phys_addr == 0) { > > + unmapped_sz += pg_size; /* Gather the size. */ > > continue; > > + } > > I guess the reason we need to validate every page is because they may > already have been legitimately mapped if someone else's reserved region > overlaps - is it worth explicitly validating that, i.e. bail out if > something's gone wrong enough that phys_addr != addr? I'm not sure the history about why to validate every page. this direct_mapping is called very early, normally after alloc_default_domain and _attach_device. the "phys_addr != addr" looks impossible. If there is a normal flow that may cause "phys_addr != addr", then something go wrong, Could we give a warning like adding a WARN_ON_ONCE(phys_addr != addr)? and it should be in a another patch. > > Other than the naming issue (I agree that map_size is a far, far better > choice), I don't have any strong opinions about the rest of the > implementation - I've written enough variations of this pattern to know > that there's just no "nice" way to do it in C; all you can do is shuffle > the clunkiness around :) :). I will send a v2. Thanks. > > Robin. > > > > > - ret = iommu_map(domain, addr, addr, pg_size, entry->prot); > > + if (unmapped_sz) { > > + /* Map the region before the overlap. */ > > + ret = iommu_map(domain, start, start, > > + unmapped_sz, entry->prot); > > + if (ret) > > + goto out; > > + start += unmapped_sz; > > + unmapped_sz = 0; > > + } > > + start += pg_size; > > + } > > + if (unmapped_sz) { > > + ret = iommu_map(domain, start, start, unmapped_sz, > > + entry->prot); > > if (ret) > > goto out; > > } > > > > _______________________________________________ > Linux-mediatek mailing list > Linux-mediatek@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-mediatek _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel