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  1. 09 8月, 2016 2 次提交
  3. 05 8月, 2016 3 次提交
    • C
      drm/i915: Enable i915_gem_wait_for_idle() without holding struct_mutex · dcff85c8
      由 Chris Wilson 提交于 
      The principal motivation for this was to try and eliminate the
struct_mutex from i915_gem_suspend - but we still need to hold the mutex
current for the i915_gem_context_lost(). (The issue there is that there
may be an indirect lockdep cycle between cpu_hotplug (i.e. suspend) and
struct_mutex via the stop_machine().) For the moment, enabling last
request tracking for the engine, allows us to do busyness checking and
waiting without requiring the struct_mutex - which is useful in its own
right.

As a side-effect of having a robust means for tracking engine busyness,
we can replace our other busyness heuristic, that of comparing against
the last submitted seqno. For paranoid reasons, we have a semi-ordered
check of that seqno inside the hangchecker, which we can now improve to
an ordered check of the engine's busyness (removing a locked xchg in the
process).

v2: Pass along "bool interruptible" as being unlocked we cannot rely on
i915->mm.interruptible being stable or even under our control.
v3: Replace check Ironlake i915_gpu_busy() with the common precalculated value
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470388464-28458-6-git-send-email-chris@chris-wilson.co.uk
      dcff85c8
    • C
      drm/i915: Introduce i915_gem_active_wait_unlocked() · 2467658e
      由 Chris Wilson 提交于 
      It is useful to be able to wait on pending rendering without grabbing
the struct_mutex. We can do this by using the i915_gem_active_get_rcu()
primitive to acquire a reference to the pending request without
requiring struct_mutex, just the RCU read lock, and then call
i915_wait_request().

v2: Rebase onto new i915_gem_active_get_unlocked() semantics that take
the RCU read lock on behalf of the caller.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470388464-28458-1-git-send-email-chris@chris-wilson.co.uk
      2467658e
    • C
      drm/i915: Enable lockless lookup of request tracking via RCU · 0eafec6d
      由 Chris Wilson 提交于 
      If we enable RCU for the requests (providing a grace period where we can
inspect a "dead" request before it is freed), we can allow callers to
carefully perform lockless lookup of an active request.

However, by enabling deferred freeing of requests, we can potentially
hog a lot of memory when dealing with tens of thousands of requests per
second - with a quick insertion of a synchronize_rcu() inside our
shrinker callback, that issue disappears.

v2: Currently, it is our responsibility to handle reclaim i.e. to avoid
hogging memory with the delayed slab frees. At the moment, we wait for a
grace period in the shrinker, and block for all RCU callbacks on oom.
Suggested alternatives focus on flushing our RCU callback when we have a
certain number of outstanding request frees, and blocking on that flush
after a second high watermark. (So rather than wait for the system to
run out of memory, we stop issuing requests - both are nondeterministic.)

Paul E. McKenney wrote:

Another approach is synchronize_rcu() after some largish number of
requests.  The advantage of this approach is that it throttles the
production of callbacks at the source.  The corresponding disadvantage
is that it slows things up.

Another approach is to use call_rcu(), but if the previous call_rcu()
is still in flight, block waiting for it.  Yet another approach is
the get_state_synchronize_rcu() / cond_synchronize_rcu() pair.  The
idea is to do something like this:

        cond_synchronize_rcu(cookie);
        cookie = get_state_synchronize_rcu();

You would of course do an initial get_state_synchronize_rcu() to
get things going.  This would not block unless there was less than
one grace period's worth of time between invocations.  But this
assumes a busy system, where there is almost always a grace period
in flight.  But you can make that happen as follows:

        cond_synchronize_rcu(cookie);
        cookie = get_state_synchronize_rcu();
        call_rcu(&my_rcu_head, noop_function);

Note that you need additional code to make sure that the old callback
has completed before doing a new one.  Setting and clearing a flag
with appropriate memory ordering control suffices (e.g,. smp_load_acquire()
and smp_store_release()).

v3: More comments on compiler and processor order of operations within
the RCU lookup and discover we can use rcu_access_pointer() here instead.

v4: Wrap i915_gem_active_get_rcu() to take the rcu_read_lock itself.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: "Goel, Akash" <akash.goel@intel.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1470324762-2545-25-git-send-email-chris@chris-wilson.co.uk
      0eafec6d
  5. 04 8月, 2016 8 次提交
  7. 03 8月, 2016 2 次提交
  9. 20 7月, 2016 4 次提交