Messages in this thread Patch in this message | | | From | Akinobu Mita <> | Subject | [PATCH 1/2] x86: don't unnecessarily call dma_alloc_from_contiguous() | Date | Mon, 29 Sep 2014 00:52:03 +0900 |
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If CONFIG_DMA_CMA is enabled, dma_generic_alloc_coherent() tries to allocate memory region by dma_alloc_from_contiguous() before trying to use alloc_pages().
This wastes CMA region by small DMA-coherent buffers which can be allocated by alloc_pages(). And it also causes performance degradation, as this is trying to drive _all_ dma mapping allocations through a _very_ small window, reported by Peter Hurley.
This fixes it by trying to allocate by alloc_pages() first in dma_generic_alloc_coherent() as dma_alloc_from_contiguous should be called only for huge allocation.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Reported-by: Peter Hurley <peter@hurleysoftware.com> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: Marek Szyprowski <m.szyprowski@samsung.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Don Dutile <ddutile@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Yinghai Lu <yinghai@kernel.org> Cc: x86@kernel.org Cc: iommu@lists.linux-foundation.org --- arch/x86/kernel/pci-dma.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c index a25e202..0402266 100644 --- a/arch/x86/kernel/pci-dma.c +++ b/arch/x86/kernel/pci-dma.c @@ -99,20 +99,20 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size, flag &= ~__GFP_ZERO; again: - page = NULL; + page = alloc_pages_node(dev_to_node(dev), flag | __GFP_NOWARN, + get_order(size)); /* CMA can be used only in the context which permits sleeping */ - if (flag & __GFP_WAIT) { + if (!page && (flag & __GFP_WAIT)) { page = dma_alloc_from_contiguous(dev, count, get_order(size)); if (page && page_to_phys(page) + size > dma_mask) { dma_release_from_contiguous(dev, page, count); page = NULL; } } - /* fallback */ - if (!page) - page = alloc_pages_node(dev_to_node(dev), flag, get_order(size)); - if (!page) + if (!page) { + warn_alloc_failed(flag, get_order(size), NULL); return NULL; + } addr = page_to_phys(page); if (addr + size > dma_mask) { -- 1.9.1
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