[Intel-gfx] [PATCH 3/3] drm/i915: Wait for the previous RCU grace period, not request completion

[Tvrtko Ursulin]

On 13/09/2018 12:18, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2018-09-13 12:16:42)
>>
>> On 12/09/2018 17:40, Chris Wilson wrote:
>>> Under mempressure, our goal is to allow ourselves sufficient time to
>>> reclaim the RCU protected slabs without overly penalizing our clients.
>>> Currently, we use a 1 jiffie wait if the client is still active as a
>>> means of throttling the allocations, but we can instead wait for the end
>>> of the RCU grace period of the clients previous allocation.
>>
>> Why did you opt for three patches changing the same code and just squash
>> to last?
> 
> 1 introduced a timeout, 2 limited it to the single timeline, 3 changed
> what we are waiting on entirely. Each of those are big jumps, and only
> (1) is required to fix the bug.

I completely understand that, just question why we want to review all 
the intermediate solutions only to end up with superior one in terms of 
both logic, design and simplicity.

Because as said before, I don't really approve of patch 1 that much, 
even if it fixes a bug.

Two is already superior, but three is right to the point of what problem 
you want to solve. (Even if I haven't looked into the exact RCU API yet, 
but it looks believable.)

Anyway, I'll let the other guys comment, maybe it is just me who is too 
picky.

Regards,

Tvrtko