From nobody Tue Feb 10 00:22:22 2026 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 43D0DC77B6D for ; Wed, 29 Mar 2023 07:25:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230089AbjC2HZa (ORCPT ); Wed, 29 Mar 2023 03:25:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60376 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230062AbjC2HZE (ORCPT ); Wed, 29 Mar 2023 03:25:04 -0400 Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B84D33AAB for ; Wed, 29 Mar 2023 00:24:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1680074689; x=1711610689; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=eFmVjsv1DCN0/J2TIleZPCjZ8XDr2WxmZ0GRJxV4ib4=; b=MpYoHoxw9PEqj+2dJV4c16PeWhTrcRwRmIQdY9HLSWfKMY3N2xrT49JR lTRD9KE3HKEDMZ1BDqWm4Ti20HxGK9F6iB2fDK9b5z2oVCiHxBbanriT9 +zIUcBLtQDmGHB8ilsnu0GVqtKB5Ohc4tToxl3/qbIy1KbK2pPuoRAxLu FpvgwGGnbdST+y7sgEKuKOFkQLMajUeWNJztX9qrvrV0zPqAvwhR484jo ppl4rMoL4ZthsV3+fwidt/lfwbtdcLqAhRXaPk4UqIAukHJdayiWwl7OB 2UwtQYklg6WwVmmpGtUafbIOkQHzBTeW+mCrm+RNxIDgV6rgS/LIgGwfk w==; X-IronPort-AV: E=McAfee;i="6600,9927,10663"; a="405746032" X-IronPort-AV: E=Sophos;i="5.98,300,1673942400"; d="scan'208";a="405746032" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Mar 2023 00:24:39 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10663"; a="684160597" X-IronPort-AV: E=Sophos;i="5.98,300,1673942400"; d="scan'208";a="684160597" Received: from liuzhao-optiplex-7080.sh.intel.com ([10.239.160.112]) by orsmga002.jf.intel.com with ESMTP; 29 Mar 2023 00:24:34 -0700 From: Zhao Liu To: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Daniel Vetter , Matthew Auld , =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= , Nirmoy Das , Maarten Lankhorst , Chris Wilson , =?UTF-8?q?Christian=20K=C3=B6nig?= , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: Ira Weiny , "Fabio M . De Francesco" , Zhenyu Wang , Zhao Liu , Dave Hansen Subject: [PATCH v2 5/9] drm/i915: Use kmap_local_page() in gem/selftests/i915_gem_coherency.c Date: Wed, 29 Mar 2023 15:32:16 +0800 Message-Id: <20230329073220.3982460-6-zhao1.liu@linux.intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230329073220.3982460-1-zhao1.liu@linux.intel.com> References: <20230329073220.3982460-1-zhao1.liu@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Zhao Liu The use of kmap_atomic() is being deprecated in favor of kmap_local_page()[1], and this patch converts the call from kmap_atomic() to kmap_local_page(). The main difference between atomic and local mappings is that local mappings doesn't disable page faults or preemption (the preemption is disabled for !PREEMPT_RT case, otherwise it only disables migration).. With kmap_local_page(), we can avoid the often unwanted side effect of unnecessary page faults or preemption disables. In drm/i915/gem/selftests/i915_gem_coherency.c, functions cpu_set() and cpu_get() mainly uses mapping to flush cache and assign the value. There're 2 reasons why cpu_set() and cpu_get() don't need to disable pagefaults and preemption for mapping: 1. The flush operation is safe. cpu_set() and cpu_get() call drm_clflush_virt_range() to use CLFLUSHOPT or WBINVD to flush. Since CLFLUSHOPT is global on x86 and WBINVD is called on each cpu in drm_clflush_virt_range(), the flush operation is global. 2. Any context switch caused by preemption or page faults (page fault may cause sleep) doesn't affect the validity of local mapping. Therefore, cpu_set() and cpu_get() are functions where the use of kmap_local_page() in place of kmap_atomic() is correctly suited. Convert the calls of kmap_atomic() / kunmap_atomic() to kmap_local_page() / kunmap_local(). [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com v2: * Dropped hot plug related description since it has nothing to do with kmap_local_page(). * No code change since v1, and added description of the motivation of using kmap_local_page(). Suggested-by: Dave Hansen Suggested-by: Ira Weiny Suggested-by: Fabio M. De Francesco Signed-off-by: Zhao Liu Reviewed-by: Ira Weiny --- Suggested by credits: Dave: Referred to his explanation about cache flush. Ira: Referred to his task document, review comments and explanation about cache flush. Fabio: Referred to his boiler plate commit message and his description about why kmap_local_page() should be preferred. --- .../gpu/drm/i915/gem/selftests/i915_gem_coherency.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c b/driv= ers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c index 3bef1beec7cb..beeb3e12eccc 100644 --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c @@ -24,7 +24,6 @@ static int cpu_set(struct context *ctx, unsigned long off= set, u32 v) { unsigned int needs_clflush; struct page *page; - void *map; u32 *cpu; int err; =20 @@ -34,8 +33,7 @@ static int cpu_set(struct context *ctx, unsigned long off= set, u32 v) goto out; =20 page =3D i915_gem_object_get_page(ctx->obj, offset >> PAGE_SHIFT); - map =3D kmap_atomic(page); - cpu =3D map + offset_in_page(offset); + cpu =3D kmap_local_page(page) + offset_in_page(offset); =20 if (needs_clflush & CLFLUSH_BEFORE) drm_clflush_virt_range(cpu, sizeof(*cpu)); @@ -45,7 +43,7 @@ static int cpu_set(struct context *ctx, unsigned long off= set, u32 v) if (needs_clflush & CLFLUSH_AFTER) drm_clflush_virt_range(cpu, sizeof(*cpu)); =20 - kunmap_atomic(map); + kunmap_local(cpu); i915_gem_object_finish_access(ctx->obj); =20 out: @@ -57,7 +55,6 @@ static int cpu_get(struct context *ctx, unsigned long off= set, u32 *v) { unsigned int needs_clflush; struct page *page; - void *map; u32 *cpu; int err; =20 @@ -67,15 +64,14 @@ static int cpu_get(struct context *ctx, unsigned long o= ffset, u32 *v) goto out; =20 page =3D i915_gem_object_get_page(ctx->obj, offset >> PAGE_SHIFT); - map =3D kmap_atomic(page); - cpu =3D map + offset_in_page(offset); + cpu =3D kmap_local_page(page) + offset_in_page(offset); =20 if (needs_clflush & CLFLUSH_BEFORE) drm_clflush_virt_range(cpu, sizeof(*cpu)); =20 *v =3D *cpu; =20 - kunmap_atomic(map); + kunmap_local(cpu); i915_gem_object_finish_access(ctx->obj); =20 out: --=20 2.34.1