From patchwork Wed Mar 29 07:32:19 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Zhao Liu X-Patchwork-Id: 13192041 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 7B8BDC74A5B for ; Wed, 29 Mar 2023 07:25:26 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 1442510EA43; Wed, 29 Mar 2023 07:25:24 +0000 (UTC) Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by gabe.freedesktop.org (Postfix) with ESMTPS id 854F010E4FC; Wed, 29 Mar 2023 07:25:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1680074711; x=1711610711; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=yyQdMm9uqDdypEaS6stlmLE4TXLEkbMEIetdKqrgHwo=; b=bSyXGX8cxPQVQWKpTE/dinL+UwzUNj/aOKgjgwggttx3gWWQrLPSKoEL Qn2L0b6IQbdksNH01hWtMGK4zNrt4aKX5T5Go1qmAFSvjcpr4A50szHEq JfeEtTJa7H+ro73xACenAbnal/Q0ATXcI+XWfhKt9ezjs5GjJb5qJ+JXF i+hKH1tzuR2ZC0RUj5i4hqLPxST0FoZCWUBhdg0oD9RkB/akDZtt113Za EhPoHn9IEF3mD6qHL9j/nwvqJuDM1BXogxNoiNitMPRgSNAmwgfYIpDE5 RoDOWsSF6HjBl5u2pNi3CegRWYduuj118zM6btY+NE+K3J1jWxEFGlflB Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10663"; a="405746229" X-IronPort-AV: E=Sophos;i="5.98,300,1673942400"; d="scan'208";a="405746229" 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 00:24:55 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10663"; a="684160648" X-IronPort-AV: E=Sophos;i="5.98,300,1673942400"; d="scan'208";a="684160648" Received: from liuzhao-optiplex-7080.sh.intel.com ([10.239.160.112]) by orsmga002.jf.intel.com with ESMTP; 29 Mar 2023 00:24:50 -0700 From: Zhao Liu To: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Daniel Vetter , Matthew Auld , =?utf-8?q?Thomas_Hellstr=C3=B6m?= , Nirmoy Das , Maarten Lankhorst , Chris Wilson , =?utf-8?q?Christian_K=C3=B6nig?= , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Date: Wed, 29 Mar 2023 15:32:19 +0800 Message-Id: <20230329073220.3982460-9-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 Subject: [Intel-gfx] [PATCH v2 8/9] drm/i915: Use kmap_local_page() in i915_cmd_parser.c 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: "Fabio M . De Francesco" , Ira Weiny , Zhao Liu , Zhenyu Wang , Dave Hansen Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" 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 and preemption disables. There're 2 reasons why function copy_batch() doesn't need to disable pagefaults and preemption for mapping: 1. The flush operation is safe. In i915_cmd_parser.c, copy_batch() calls 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, copy_batch() is a function 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. --- drivers/gpu/drm/i915/i915_cmd_parser.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c index ddf49c2dbb91..2905df83e180 100644 --- a/drivers/gpu/drm/i915/i915_cmd_parser.c +++ b/drivers/gpu/drm/i915/i915_cmd_parser.c @@ -1211,11 +1211,11 @@ static u32 *copy_batch(struct drm_i915_gem_object *dst_obj, for (n = offset >> PAGE_SHIFT; remain; n++) { int len = min(remain, PAGE_SIZE - x); - src = kmap_atomic(i915_gem_object_get_page(src_obj, n)); + src = kmap_local_page(i915_gem_object_get_page(src_obj, n)); if (src_needs_clflush) drm_clflush_virt_range(src + x, len); memcpy(ptr, src + x, len); - kunmap_atomic(src); + kunmap_local(src); ptr += len; remain -= len;