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drm/prime: skip CPU sync in map/unmap dma_buf

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Dma-bufs should already be device coherent, as they are only pulled in the
CPU domain via the begin/end cpu_access calls. As we cache the mapping set
up by dma_map_sg a CPU sync at this point will not actually guarantee proper
coherency on non-coherent architectures, so we can as well stop pretending.

This is an important performance fix for architectures which need explicit
cache synchronization and userspace doing lots of dma-buf imports.
Improves Weston on Etnaviv performance 5x, where before this patch > 90%
of Weston CPU time was spent synchronizing caches for buffers which are
already device coherent.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171130173428.8666-1-l.stach@pengutronix.de
This commit is contained in:
Lucas Stach 2017-11-30 18:34:28 +01:00 committed by Daniel Vetter
parent b57e8b7661
commit ca0e68e21a
1 changed files with 5 additions and 3 deletions
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8
drivers/gpu/drm/drm_prime.c
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@ -218,8 +218,9 @@ static void drm_gem_map_detach(struct dma_buf *dma_buf,
sgt = prime_attach->sgt;
if (sgt) {
if (prime_attach->dir != DMA_NONE)
dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents,
prime_attach->dir);
dma_unmap_sg_attrs(attach->dev, sgt->sgl, sgt->nents,
prime_attach->dir,
DMA_ATTR_SKIP_CPU_SYNC);
sg_free_table(sgt);
}
@ -277,7 +278,8 @@ static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
sgt = obj->dev->driver->gem_prime_get_sg_table(obj);
if (!IS_ERR(sgt)) {
if (!dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir)) {
if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
DMA_ATTR_SKIP_CPU_SYNC)) {
sg_free_table(sgt);
kfree(sgt);
sgt = ERR_PTR(-ENOMEM);