On Wed, 19 Apr 2023 at 11:05, Petr Tesarik <petrtesarik@xxxxxxxxxxxxxxx> wrote: > > From: Petr Tesarik <petr.tesarik.ext@xxxxxxxxxx> > > The goal of my work is to provide more flexibility in the sizing of > SWIOTLB. > > The software IO TLB was designed with these assumptions: > > 1. It would not be used much, especially on 64-bit systems. > 2. A small fixed memory area (64 MiB by default) is sufficient to > handle the few cases which require a bounce buffer. > 3. 64 MiB is little enough that it has no impact on the rest of the > system. > > First, if SEV is active, all DMA must be done through shared > unencrypted pages, and SWIOTLB is used to make this happen without > changing device drivers. The software IO TLB size is increased to > 6% of total memory in sev_setup_arch(), but that is more of an > approximation. The actual requirements may vary depending on the > amount of I/O and which drivers are used. These factors may not be > know at boot time, i.e. when SWIOTLB is allocated. > > Second, other colleagues have noticed that they can reliably get > rid of occasional OOM kills on an Arm embedded device by reducing > the SWIOTLB size. This can be achieved with a kernel parameter, but > determining the right value puts additional burden on pre-release > testing, which could be avoided if SWIOTLB is allocated small and > grows only when necessary. > > Changes from v1-devel-v7: > - Add comments to acquire/release barriers > - Fix whitespace issues reported by checkpatch.pl > > Changes from v1-devel-v6: > - Provide long description of functions > - Fix kernel-doc (Returns: to Return:) > - Rename __lookup_dyn_slot() to lookup_dyn_slot_locked() > > Changes from RFC: > - Track dynamic buffers per device instead of per swiotlb > - Use a linked list instead of a maple tree > - Move initialization of swiotlb fields of struct device to a > helper function > - Rename __lookup_dyn_slot() to lookup_dyn_slot_locked() > - Introduce per-device flag if dynamic buffers are in use > - Add one more user of DMA_ATTR_MAY_SLEEP > - Add kernel-doc comments for new (and some old) code > - Properly escape '*' in dma-attributes.rst > > Petr Tesarik (7): > swiotlb: Use a helper to initialize swiotlb fields in struct device > swiotlb: Move code around in preparation for dynamic bounce buffers > dma-mapping: introduce the DMA_ATTR_MAY_SLEEP attribute > swiotlb: Dynamically allocated bounce buffers > swiotlb: Add a boot option to enable dynamic bounce buffers > drm: Use DMA_ATTR_MAY_SLEEP from process context > swiotlb: per-device flag if there are dynamically allocated buffers > > .../admin-guide/kernel-parameters.txt | 6 +- > Documentation/core-api/dma-attributes.rst | 10 + > drivers/base/core.c | 4 +- > drivers/gpu/drm/drm_gem_shmem_helper.c | 2 +- > drivers/gpu/drm/drm_prime.c | 2 +- > include/linux/device.h | 12 + > include/linux/dma-mapping.h | 6 + > include/linux/swiotlb.h | 54 ++- > kernel/dma/swiotlb.c | 382 ++++++++++++++++-- > 9 files changed, 443 insertions(+), 35 deletions(-) > > -- > 2.25.1 > Hi Is this a potential fix for https://bugzilla.kernel.org/show_bug.cgi?id=217310 where I'm manually setting bigger buffers to keep my wifi working? Thanks Mike
