From: Leonardo Bras <leobras.c@gmail.com>
To: Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Alexey Kardashevskiy <aik@ozlabs.ru>,
Nicolin Chen <nicoleotsuka@gmail.com>,
Niklas Schnelle <schnelle@linux.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] powerpc/kernel/iommu: Align size for IOMMU_PAGE_SIZE() to save TCEs
Date: Thu, 22 Apr 2021 03:53:13 -0300 [thread overview]
Message-ID: <2f985cdb2a62c52ce2a26118f1966c00176cc4b9.camel@gmail.com> (raw)
In-Reply-To: <20210318174414.684630-1-leobras.c@gmail.com>
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 <leobras.c@gmail.com>
> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> 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));
next prev parent reply other threads:[~2021-04-22 6:53 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 17:44 [PATCH 1/1] powerpc/kernel/iommu: Align size for IOMMU_PAGE_SIZE() to save TCEs Leonardo Bras
2021-03-18 17:44 ` [PATCH 1/1] powerpc/kernel/iommu: Use largepool as a last resort when !largealloc Leonardo Bras
2021-04-22 6:50 ` Leonardo Bras
2021-04-29 14:01 ` Michael Ellerman
2021-04-22 6:53 ` Leonardo Bras [this message]
2021-04-29 14:01 ` [PATCH 1/1] powerpc/kernel/iommu: Align size for IOMMU_PAGE_SIZE() to save TCEs Michael Ellerman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=2f985cdb2a62c52ce2a26118f1966c00176cc4b9.camel@gmail.com \
--to=leobras.c@gmail.com \
--cc=aik@ozlabs.ru \
--cc=benh@kernel.crashing.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mpe@ellerman.id.au \
--cc=nicoleotsuka@gmail.com \
--cc=paulus@samba.org \
--cc=schnelle@linux.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).