> -----Original Message----- > From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Sent: Thursday, October 15, 2020 8:07 AM > To: Tang, CQ <cq.tang@xxxxxxxxx>; intel-gfx@xxxxxxxxxxxxxxxxxxxxx > Subject: Re: [PATCH] drm/i915: Make the GEM reclaim workqueue > high priority > > Quoting Tang, CQ (2020-10-14 00:29:13) > > i915_gem_free_object() is called by multiple threads/processes, they all > add objects onto the same free_list. The free_list processing worker thread > becomes bottle-neck. I see that the worker is mostly a single thread (with > particular thread ID), but sometimes multiple threads are launched to > process the 'free_list' work concurrently. But the processing speed is still > slower than the multiple process's feeding speed, and 'free_list' is holding > more and more memory. > > We can also prune the free_list immediately, if we know we are outside of > any critical section. (We do this before create ioctls, and I thought upon > close(device), but I see that's just contexts.) > > > The worker launching time is delayed a lot, we call queue_work() when we > add the first object onto the empty 'free_list', but when the worker is > launched, the 'free_list' has sometimes accumulated 1M objects. Maybe it is > because of waiting currently running worker to finish? > > 1M is a lot more than is comfortable, and that's even with a high-priority > worker. The problem with objects being freed from any context is that we > can't simply put a flush_work around there. (Not without ridding ourselves of > a few mutexes at least.) We could try more than worker, but it's no more > more effort to starve 2 cpus than it is to starve 1. > > No, with that much pressure the only option is to apply the backpressure at > the point of allocation ala create_ioctl. i.e. find the hog, and look to see if > there's a convenient spot before/after to call > i915_gem_flush_free_objects(). Since you highlight the vma-stash as the > likely culprit, and the free_pt_stash is unlikely to be inside any critical section, > might as well try flushing from there for starters. I have not yet tested, but I guess calling i915_gem_flush_free_objects() inside free_pt_stash() will solve the problem that gem_exec_gttfill has, because it will give some back pressure on the system traffic. But this is only for the page table 4K lmem objects allocated/freed by vma-stash. We might encounter the same situation with user space allocated objects. --CQ > > Hmm, actually we are tantalizing close to having dropped all mutexes (and > similar global lock-like effects) from free_objects. That would be a nice > victory. > -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
