From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.5 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 573E5C07E9B for ; Mon, 19 Jul 2021 13:35:16 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0DB3860FF4 for ; Mon, 19 Jul 2021 13:35:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0DB3860FF4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 70FA289E05; Mon, 19 Jul 2021 13:35:13 +0000 (UTC) Received: from mail-qk1-x730.google.com (mail-qk1-x730.google.com [IPv6:2607:f8b0:4864:20::730]) by gabe.freedesktop.org (Postfix) with ESMTPS id E768489E5A; Mon, 19 Jul 2021 13:35:11 +0000 (UTC) Received: by mail-qk1-x730.google.com with SMTP id m3so16637894qkm.10; Mon, 19 Jul 2021 06:35:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=EC2ljfPhA7WIDSKlhsiohqQaEAYTTTn3yjJVmX2LV28=; b=bLuSQuT2M+a5nFk2Me/nOHiiVX6Orri2c+U3h9Na+XttZwglYQQDVxawe7l8K2Pegb XAyCMLu6b2zT3ya7BeYLPCqEqN+A0yzYirNUKGAYp3+b3U2FQJHzaHfHQonou7c4YBvi hEga8Rw4emRB47yZ12McgTZGS7jA9cHp5GATuMv9pORNozygUDrn1aOJJqh4/4y89BI0 I9E6l7LIl8hANVWqqrr3IwiBggfDktqn6mvEJ0/ohMgeOKPZaMkXKBi0Zzo5us5DgX6F bEZ2ljXM0KtemTfVXAP9x4ann15ikMxsft7oKTn6G0OlYTmfFwRwWLcQSQiOqatknl7z 3Jvg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=EC2ljfPhA7WIDSKlhsiohqQaEAYTTTn3yjJVmX2LV28=; b=mTgAv1VrsqEYL7haWt9QgBBcFyFHpRfCUDiBFq/gC6m/MhCPwQ2Ude8Vmm+u7BpYeA HQ+hQJYrXf+f0Cvyd8Xh/n1WXG+lMfzXyhJGXktBhLZ1mrHsYNllLZkq793WTLhswx3m hsUJrNZrmSvs9XePw25egu4Wv/aVK8hPOCbs8q1paC6VPJ1KLvFkqnl4iHJgqLYNCOR2 hoDc6wNmhh5CxfOgq5QQul11CFyXtjtZ7tXBgYZCA1YrobK62BP12fkpIIjhGEaS2S0p 8+Pj1l5N5B5DoPYFgA0DH1mopSEBKRHE9cYvAQ0vNkYibIFJGXgaUoT4P9KbWM6FbUXs 0/SQ== X-Gm-Message-State: AOAM531u/WHTYomgN4KadxxmoK831VZbBbLh9A+NzcxTwkRX73HCGsz9 pwvcPee+np2mPmR+Qw0ZHJbBkMGHgplR0tuqggQ= X-Google-Smtp-Source: ABdhPJxmlNIAov9jv6/V1smJnZGisiGgPH3TLoJDAd6Ay8dmK9t28mtcCUK3I6F1pQg3s+l6aTy2GYSSowFwKcULCEw= X-Received: by 2002:a05:620a:1581:: with SMTP id d1mr23120175qkk.327.1626701710283; Mon, 19 Jul 2021 06:35:10 -0700 (PDT) MIME-Version: 1.0 References: <20210715223900.1840576-1-jason@jlekstrand.net> <20210715223900.1840576-6-jason@jlekstrand.net> In-Reply-To: From: Matthew Auld Date: Mon, 19 Jul 2021 14:34:44 +0100 Message-ID: To: Jason Ekstrand Subject: Re: [Intel-gfx] [PATCH 5/7] drm/i915/gem/ttm: Respect the objection region in placement_from_obj X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Intel Graphics Development , Matthew Auld , ML dri-devel Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Fri, 16 Jul 2021 at 20:49, Jason Ekstrand wrote: > > On Fri, Jul 16, 2021 at 1:45 PM Matthew Auld > wrote: > > > > On Fri, 16 Jul 2021 at 18:39, Jason Ekstrand wrote: > > > > > > On Fri, Jul 16, 2021 at 11:00 AM Matthew Auld > > > wrote: > > > > > > > > On Fri, 16 Jul 2021 at 16:52, Matthew Auld > > > > wrote: > > > > > > > > > > On Fri, 16 Jul 2021 at 15:10, Jason Ekstrand wrote: > > > > > > > > > > > > On Fri, Jul 16, 2021 at 8:54 AM Matthew Auld > > > > > > wrote: > > > > > > > > > > > > > > On Thu, 15 Jul 2021 at 23:39, Jason Ekstrand wrote: > > > > > > > > > > > > > > > > Whenever we had a user object (n_placements > 0), we were ignoring > > > > > > > > obj->mm.region and always putting obj->placements[0] as the requested > > > > > > > > region. For LMEM+SMEM objects, this was causing them to get shoved into > > > > > > > > LMEM on every i915_ttm_get_pages() even when SMEM was requested by, say, > > > > > > > > i915_gem_object_migrate(). > > > > > > > > > > > > > > i915_ttm_migrate calls i915_ttm_place_from_region() directly with the > > > > > > > requested region, so there shouldn't be an issue with migration right? > > > > > > > Do you have some more details? > > > > > > > > > > > > With i915_ttm_migrate directly, no. But, in the last patch in the > > > > > > series, we're trying to migrate LMEM+SMEM buffers into SMEM on > > > > > > attach() and pin it there. This blows up in a very unexpected (IMO) > > > > > > way. The flow goes something like this: > > > > > > > > > > > > - Client attempts a dma-buf import from another device > > > > > > - In attach() we call i915_gem_object_migrate() which calls > > > > > > i915_ttm_migrate() which migrates as requested. > > > > > > - Once the migration is complete, we call i915_gem_object_pin_pages() > > > > > > which calls i915_ttm_get_pages() which depends on > > > > > > i915_ttm_placement_from_obj() and so migrates it right back to LMEM. > > > > > > > > > > The mm.pages must be NULL here, otherwise it would just increment the > > > > > pages_pin_count? > > > > > > Given that the test is using the ____four_underscores version, it > > > doesn't have that check. However, this executes after we've done the > > > dma-buf import which pinned pages. So we should definitely have > > > pages. > > > > We shouldn't call ____four_underscores() if we might already have > > pages though. Under non-TTM that would leak the pages, and in TTM we > > might hit the WARN_ON(mm->pages) in __i915_ttm_get_pages(), if for > > example nothing was moved. I take it we can't just call pin_pages()? > > Four scary underscores usually means "don't call this in normal code". > > I've switched the ____four_underscores call to a __two_underscores in > the selftests and it had no effect, good or bad. But, still, probably > better to call that one. > > > > > > > > > > > > > > > > Maybe the problem here is actually that our TTM code isn't respecting > > > > > > obj->mm.pages_pin_count? > > > > > > > > > > I think if the resource is moved, we always nuke the mm.pages after > > > > > being notified of the move. Also TTM is also not allowed to move > > > > > pinned buffers. > > > > > > > > > > I guess if we are evicted/swapped, so assuming we are not holding the > > > > > object lock, and it's not pinned, the future call to get_pages() will > > > > > see mm.pages = NULL, even though the ttm_resource is still there, and > > > > > because we prioritise the placements[0], instead of mm.region we end > > > > > up moving it for no good reason. But in your case you are holding the > > > > > lock, or it's pinned? Also is this just with the selftest, or > > > > > something real? > > > > > > > > Or at least in the selftest I see ____i915_gem_object_get_pages() > > > > which doesn't even consider the mm.pages AFAIK. > > > > > > The bogus migration is happening as part of the > > > __i915_gem_object_get_pages() (2 __underscores) call in > > > i915_gem_dmabuf_attach (see last patch). That code is attempting to > > > migrate the BO to SMEM and then pin it there using the obvious calls > > > to do so. However, in the pin_pages call, it gets implicitly migrated > > > back to LMEM thanks to i915_ttm_get_pages(). Why is _get_pages() > > > migrating things at all? > > > > Not sure yet, but __two_underscores() checks if > > i915_gem_object_has_pages() before actually calling into > > i915_ttm_get_pages(), so the mm.pages would have to be NULL here for > > some reason, so best guess is something to do with move_notify(). > > Did a bit of experimenting along those lines and added the following > to the self-test BEFORE the export/import: > > i915_gem_object_lock(obj, NULL); > err = __i915_gem_object_get_pages(obj); > __i915_gem_object_unpin_pages(obj); > i915_gem_object_unlock(obj); > if (err) { > pr_err("__i915_gem_object_get_pages failed with err=%d\n", err); > goto out_ret; > } > > This seems to make the migration happen as expected without this > patch. So it seems the problem only exists on buffers that haven't > gotten any backing storage yet (if I'm understanding get_pages > correctly). > > One potential work-around (not sure if this is a good idea or not!) > would be to do this inside dmabuf_attach(). Is this reliable? Once > it has pages will it always have pages? Or are there crazy races I > need to be worried about here? It turns out that the i915_ttm_adjust_gem_after_move() call in ttm_object_init will always update the mm.region to system memory(so that it matches the ttm resource), which seems reasonable given the default system placeholder thing, but does seem slightly iffy since we haven't actually moved/allocated anything. So effectively i915_ttm_migrate(SYSTEM) becomes a noop here since mm.region == mr. Which ofc means when we actually call get_pages() all that happens is that we allocate the pages in system memory(or without this patch placements[0]). Also with this patch lmem+smem, will always be placed in smem first, regardless of the placements ordering. For now we could maybe just split i915_ttm_adjust_gem_after_move() so we skip the part which updates the mm.region here in the init portion, since that should only happen when we try to place the object for real? > > --Jason _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx