Re: [PATCH 5/6] drm/ttm: replace dma_resv object on deleted BOs v2

[Christian König]

Am 11.02.20 um 16:02 schrieb Pan, Xinhui:

2020年2月11日 22:14，Daniel Vetter <dan...@ffwll.ch> 写道：

On Mon, Feb 10, 2020 at 04:09:06PM +0100, Christian König wrote:
When non-imported BOs are resurrected for delayed delete we replace
the dma_resv object to allow for easy reclaiming of the resources.

v2: move that to ttm_bo_individualize_resv

Signed-off-by: Christian König <christian.koe...@amd.com>
---
drivers/gpu/drm/ttm/ttm_bo.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index d0624685f5d2..4d161038de98 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -393,6 +393,14 @@ static int ttm_bo_individualize_resv(struct 
ttm_buffer_object *bo)

        r = dma_resv_copy_fences(&bo->base._resv, bo->base.resv);
        dma_resv_unlock(&bo->base._resv);
+       if (r)
+               return r;
+
+       if (bo->type != ttm_bo_type_sg) {
+               spin_lock(&ttm_bo_glob.lru_lock);
+               bo->base.resv = &bo->base._resv;
Having the dma_resv pointer be protected by the lru_lock for ttm internal
stuff, but invariant everywhere else is really confusing. Not sure that's
I think this is reader VS writer.
To avoid any internal functions using the old resv,  using an existing spin 
lock is acceptable.
Maybe RCU is better? That will need a lot of effort.
Anyway, ttm sucks. We HAS done a lot of work on it to make it better running on 
modern system.

Yeah that summarize my recent presentation about TTM pretty much :)

Double checked that and the only reason we have the lock is that in 
ttm_mem_evict_first() we trylock first and then grab a reference.

So we should probably rework that code as well and then we can also drop 
that lock here, but that should come later.

Christian.



a great idea, I've just chased some ttm code around freaking out about
that.
-Daniel

+               spin_unlock(&ttm_bo_glob.lru_lock);
+       }

        return r;
}
@@ -720,7 +728,7 @@ static bool ttm_bo_evict_swapout_allowable(struct 
ttm_buffer_object *bo,

        if (bo->base.resv == ctx->resv) {
                dma_resv_assert_held(bo->base.resv);
-               if (ctx->flags & TTM_OPT_FLAG_ALLOW_RES_EVICT || bo->deleted)
+               if (ctx->flags & TTM_OPT_FLAG_ALLOW_RES_EVICT)
                        ret = true;
                *locked = false;
                if (busy)
--
2.17.1

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Daniel Vetter
Software Engineer, Intel Corporation
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