On Mon, Feb 22, 2010 at 08:58:28PM +0100, Thomas Hellstrom wrote:
> Jerome Glisse wrote:
> >On Mon, Feb 22, 2010 at 06:30:24PM +0100, Thomas Hellstrom wrote:
> >>Jerome Glisse wrote:
> >>>Thomas i think i addressed your concern here, the ttm_bo_validate
> >>>didn't needed a new argument or i did not understand what was
> >>>necessary beside no_wait. In this patchset we check the value
> >>>of callback in case of EBUSY (call set_need_resched) or ERESTARTSYS
> >>>we return VM_FAULT_NOPAGE.
> >>Well, if we from the fault callback call any function that might
> >>call ttm_bo_reserve or ttm_bo_reserve_locked, we must make sure
> >>that we never wait, but return -EBUSY all the way back to the
> >>fault function. Such a case may be ttm_bo_validate that calls
> >>ttm_bo_evict_first, or something causing a swapout...
> >>ttm_bo_validate currently doesn't have that functionality,
> >>because @no_wait just means don't wait for GPU.
> >
> >What do you mean by never wait ? Is this GPU wait ? or CPU wait ie don't
> >use mutex or kernel code path that might sleep ?
>
> I mean waiting while reserving a bo. (If another thread has the bo
> reserved).
>
> >After a new review i don't think we ever wait for the GPU with the current
> >patch and as far as i can tell we will return EBUSY or ERESTART all the
> >way up.
> >
> >Cheers,
> >Jerome
>
> If there is *no* code path trying to reserve a bo or create a
> user-space visible object from within the fault handler, it should
> be ok.
>
> /Thomas
>
>
Did a new review again here is the call chain :
ttm_bo_move_buffer
ttm_bo_mem_space
ttm_bo_mem_force_space
ttm_mem_evict_first
ttm_bo_reserve_locked (no_wait = true)
ttm_bo_evict
ttm_bo_mem_space
ttm_bo_handle_move_mem
(ttm_bo_unmap_virtual)
ttm_bo_add_ttm
ttm_tt_create
ttm_bo_handle_move_mem
(ttm_bo_unmap_virtual)
ttm_bo_add_ttm
ttm_tt_create
the no_wait argument is passed all the way down and whenever
there is an error or EBUSY or ERESTARTSYS it's then returned
all the way up. I am bit unconfortable with the ttm_bo_unmap_virtual
i wonder if it can cause issue. I have been looking for
information on the fault callback and what one can do or one
shouldn't do but haven't found much, do you have any pointer
beside reading core code ?
Cheers,
Jerome
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