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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7130ECA0FFC for ; Tue, 5 Sep 2023 16:04:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231246AbjIEQEM (ORCPT ); Tue, 5 Sep 2023 12:04:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41920 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353627AbjIEG4h (ORCPT ); Tue, 5 Sep 2023 02:56:37 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EF29C1B4 for ; Mon, 4 Sep 2023 23:56:32 -0700 (PDT) Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by madras.collabora.co.uk (Postfix) with ESMTPSA id 131296607186; Tue, 5 Sep 2023 07:56:31 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1693896991; bh=JHqTWW5qePWPrhtaEWzXFcu5nWOXVqNpQrMkThmLz/4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=gXixS2oxgFajfNPpnj8TqPqK4DT50LybyGhv7lKfhjj80d+yqd9ItXHUN71KsYAlr aKMf8QXxJIetgIMqYIkudi7Kv6evw14qne1/CzuIbYeYYNQGQgLBX6F1bLBksSlYHS Z5nLd9OSc6XUcibJXIlfXk0+3oh3KbKb02lzsqaWhncLjj5pBKXhyEoW5q2xML78yI 3ZZAFJJ9dYbdz14X2c19AjxRuiNNk2ZDt/xv60yEuuzeh/DkwoT5rmTC06+nczwfGb h5DtzfKFDJC9OwY5INqI007hbfhqHMs0y4QhaH3hP/wxUrQqWYABBGhdodi2hspmjX Z0gN5TgrHt6Ig== Date: Tue, 5 Sep 2023 08:56:28 +0200 From: Boris Brezillon To: Dmitry Osipenko Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Christian =?UTF-8?B?S8O2bmln?= , Qiang Yu , Steven Price , Emma Anholt , Melissa Wen , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v16 11/20] drm/shmem-helper: Use refcount_t for pages_use_count Message-ID: <20230905085628.4cf50ace@collabora.com> In-Reply-To: <20230903170736.513347-12-dmitry.osipenko@collabora.com> References: <20230903170736.513347-1-dmitry.osipenko@collabora.com> <20230903170736.513347-12-dmitry.osipenko@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 3 Sep 2023 20:07:27 +0300 Dmitry Osipenko wrote: > Use atomic refcount_t helper for pages_use_count to optimize pin/unpin > functions by skipping reservation locking while GEM's pin refcount > 1. > > Suggested-by: Boris Brezillon > Signed-off-by: Dmitry Osipenko > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++-------------- > drivers/gpu/drm/lima/lima_gem.c | 2 +- > drivers/gpu/drm/panfrost/panfrost_mmu.c | 2 +- > include/drm/drm_gem_shmem_helper.h | 2 +- > 4 files changed, 19 insertions(+), 22 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index 7e1e674e2c9f..a0faef3e762d 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -152,12 +152,12 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > sg_free_table(shmem->sgt); > kfree(shmem->sgt); > } > - if (shmem->pages) { > + if (refcount_read(&shmem->pages_use_count)) { As explained in my v15 review, I'm not convinced this is the right thing to do. We should instead move the drm_gem_shmem_put_pages_locked() call in the preceding 'if (shmem->sgt)' block, because the sgt creation logic is where this implicit pages ref was taken. If shmem->sgt == NULL, there's no reason to call drm_gem_shmem_put_pages_locked() and we should let the following drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count)) complain. Besides, I don't think this change should be part of the uint -> refcount_t conversion. > drm_gem_shmem_put_pages_locked(shmem); > drm_WARN_ON(obj->dev, !shmem->got_pages_sgt); > } > > - drm_WARN_ON(obj->dev, shmem->pages_use_count); > + drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count)); > > dma_resv_unlock(shmem->base.resv); > } > @@ -174,14 +174,13 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem) > > dma_resv_assert_held(shmem->base.resv); > > - if (shmem->pages_use_count++ > 0) > + if (refcount_inc_not_zero(&shmem->pages_use_count)) > return 0; > > pages = drm_gem_get_pages(obj); > if (IS_ERR(pages)) { > drm_dbg_kms(obj->dev, "Failed to get pages (%ld)\n", > PTR_ERR(pages)); > - shmem->pages_use_count = 0; > return PTR_ERR(pages); > } > > @@ -197,6 +196,8 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem) > > shmem->pages = pages; > > + refcount_set(&shmem->pages_use_count, 1); > + > return 0; > } > > @@ -212,21 +213,17 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) > > dma_resv_assert_held(shmem->base.resv); > > - if (drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count)) > - return; > - > - if (--shmem->pages_use_count > 0) > - return; > - > + if (refcount_dec_and_test(&shmem->pages_use_count)) { > #ifdef CONFIG_X86 > - if (shmem->map_wc) > - set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT); > + if (shmem->map_wc) > + set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT); > #endif > > - drm_gem_put_pages(obj, shmem->pages, > - shmem->pages_mark_dirty_on_put, > - shmem->pages_mark_accessed_on_put); > - shmem->pages = NULL; > + drm_gem_put_pages(obj, shmem->pages, > + shmem->pages_mark_dirty_on_put, > + shmem->pages_mark_accessed_on_put); > + shmem->pages = NULL; > + } > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked); > > @@ -553,8 +550,8 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma) > * mmap'd, vm_open() just grabs an additional reference for the new > * mm the vma is getting copied into (ie. on fork()). > */ > - if (!drm_WARN_ON_ONCE(obj->dev, !shmem->pages_use_count)) > - shmem->pages_use_count++; > + drm_WARN_ON_ONCE(obj->dev, > + !refcount_inc_not_zero(&shmem->pages_use_count)); > > dma_resv_unlock(shmem->base.resv); > > @@ -642,7 +639,7 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem, > return; > > drm_printf_indent(p, indent, "pages_pin_count=%u\n", refcount_read(&shmem->pages_pin_count)); > - drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count); > + drm_printf_indent(p, indent, "pages_use_count=%u\n", refcount_read(&shmem->pages_use_count)); > drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count); > drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr); > } > diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c > index ec8f718aa539..4be2fccbf6d9 100644 > --- a/drivers/gpu/drm/lima/lima_gem.c > +++ b/drivers/gpu/drm/lima/lima_gem.c > @@ -47,8 +47,8 @@ int lima_heap_alloc(struct lima_bo *bo, struct lima_vm *vm) > } > > bo->base.pages = pages; > - bo->base.pages_use_count = 1; > bo->base.got_pages_sgt = true; > + refcount_set(&bo->base.pages_use_count, 1); > > mapping_set_unevictable(mapping); > } > diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c > index 7771769f0ce0..a91252053aa3 100644 > --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c > +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c > @@ -487,7 +487,7 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as, > goto err_unlock; > } > bo->base.pages = pages; > - bo->base.pages_use_count = 1; > + refcount_set(&bo->base.pages_use_count, 1); > } else { > pages = bo->base.pages; > if (pages[page_offset]) { > diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h > index 1cd74ae5761a..bd545428a7ee 100644 > --- a/include/drm/drm_gem_shmem_helper.h > +++ b/include/drm/drm_gem_shmem_helper.h > @@ -37,7 +37,7 @@ struct drm_gem_shmem_object { > * Reference count on the pages table. > * The pages are put when the count reaches zero. > */ > - unsigned int pages_use_count; > + refcount_t pages_use_count; > > /** > * @pages_pin_count: