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Wed, 21 Apr 2021 23:53:16 -0700 (PDT) Message-ID: <2f985cdb2a62c52ce2a26118f1966c00176cc4b9.camel@gmail.com> Subject: Re: [PATCH 1/1] powerpc/kernel/iommu: Align size for IOMMU_PAGE_SIZE() to save TCEs From: Leonardo Bras To: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Alexey Kardashevskiy , Nicolin Chen , Niklas Schnelle Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Date: Thu, 22 Apr 2021 03:53:13 -0300 In-Reply-To: <20210318174414.684630-1-leobras.c@gmail.com> References: <20210318174414.684630-1-leobras.c@gmail.com> Organization: IBM Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.38.4 (3.38.4-1.fc33) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, This patch was also reviewed when it was part of another patchset: http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20200911170738.82818-4-leobras.c@gmail.com/ On Thu, 2021-03-18 at 14:44 -0300, Leonardo Bras wrote: > Currently both iommu_alloc_coherent() and iommu_free_coherent() align the > desired allocation size to PAGE_SIZE, and gets system pages and IOMMU > mappings (TCEs) for that value. > > When IOMMU_PAGE_SIZE < PAGE_SIZE, this behavior may cause unnecessary > TCEs to be created for mapping the whole system page. > > Example: > - PAGE_SIZE = 64k, IOMMU_PAGE_SIZE() = 4k > - iommu_alloc_coherent() is called for 128 bytes > - 1 system page (64k) is allocated > - 16 IOMMU pages (16 x 4k) are allocated (16 TCEs used) > > It would be enough to use a single TCE for this, so 15 TCEs are > wasted in the process. > > Update iommu_*_coherent() to make sure the size alignment happens only > for IOMMU_PAGE_SIZE() before calling iommu_alloc() and iommu_free(). > > Also, on iommu_range_alloc(), replace ALIGN(n, 1 << tbl->it_page_shift) > with IOMMU_PAGE_ALIGN(n, tbl), which is easier to read and does the > same. > > Signed-off-by: Leonardo Bras > Reviewed-by: Alexey Kardashevskiy > --- >  arch/powerpc/kernel/iommu.c | 11 ++++++----- >  1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c > index 5b69a6a72a0e..3329ef045805 100644 > --- a/arch/powerpc/kernel/iommu.c > +++ b/arch/powerpc/kernel/iommu.c > @@ -851,6 +851,7 @@ void *iommu_alloc_coherent(struct device *dev, struct iommu_table *tbl, >   unsigned int order; >   unsigned int nio_pages, io_order; >   struct page *page; > + size_t size_io = size; >   > >   size = PAGE_ALIGN(size); >   order = get_order(size); > @@ -877,8 +878,9 @@ void *iommu_alloc_coherent(struct device *dev, struct iommu_table *tbl, >   memset(ret, 0, size); >   > >   /* Set up tces to cover the allocated range */ > - nio_pages = size >> tbl->it_page_shift; > - io_order = get_iommu_order(size, tbl); > + size_io = IOMMU_PAGE_ALIGN(size_io, tbl); > + nio_pages = size_io >> tbl->it_page_shift; > + io_order = get_iommu_order(size_io, tbl); >   mapping = iommu_alloc(dev, tbl, ret, nio_pages, DMA_BIDIRECTIONAL, >   mask >> tbl->it_page_shift, io_order, 0); >   if (mapping == DMA_MAPPING_ERROR) { > @@ -893,10 +895,9 @@ void iommu_free_coherent(struct iommu_table *tbl, size_t size, >   void *vaddr, dma_addr_t dma_handle) >  { >   if (tbl) { > - unsigned int nio_pages; > + size_t size_io = IOMMU_PAGE_ALIGN(size, tbl); > + unsigned int nio_pages = size_io >> tbl->it_page_shift; >   > > - size = PAGE_ALIGN(size); > - nio_pages = size >> tbl->it_page_shift; >   iommu_free(tbl, dma_handle, nio_pages); >   size = PAGE_ALIGN(size); >   free_pages((unsigned long)vaddr, get_order(size));