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 71AC0EB64D8 for ; Wed, 21 Jun 2023 18:51:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231287AbjFUSvw (ORCPT ); Wed, 21 Jun 2023 14:51:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38096 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229472AbjFUSvt (ORCPT ); Wed, 21 Jun 2023 14:51:49 -0400 Received: from ste-pvt-msa2.bahnhof.se (ste-pvt-msa2.bahnhof.se [213.80.101.71]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E8C25199B for ; Wed, 21 Jun 2023 11:51:44 -0700 (PDT) Received: from localhost (localhost [127.0.0.1]) by ste-pvt-msa2.bahnhof.se (Postfix) with ESMTP id C1BC03F338; Wed, 21 Jun 2023 20:51:42 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at bahnhof.se Authentication-Results: ste-pvt-msa2.bahnhof.se (amavisd-new); dkim=pass (1024-bit key) header.d=shipmail.org Received: from ste-pvt-msa2.bahnhof.se ([127.0.0.1]) by localhost (ste-pvt-msa2.bahnhof.se [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 3-gXWQQZVyex; Wed, 21 Jun 2023 20:51:42 +0200 (CEST) Received: by ste-pvt-msa2.bahnhof.se (Postfix) with ESMTPA id 774123F23E; Wed, 21 Jun 2023 20:51:40 +0200 (CEST) Received: from [192.168.0.209] (unknown [134.191.232.81]) by mail1.shipmail.org (Postfix) with ESMTPSA id 9061E3631FC; Wed, 21 Jun 2023 20:51:36 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=shipmail.org; s=mail; t=1687373500; bh=UZ9dLzxvn9rMplig/F09sFuaqVn4QOtCtPf3MFkS8iM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=efkLibh8YRkRPojkYXPtoahK5+L9pTTxJFwWFY/E5z1KuLwVRIS1Ol/XayUG0SLw2 4kPzN99a7iL/03cbcnusyeI7k9kWmZxSVsWPX00sJFSDsfVQ75/eolEVNOYBghgITU w+jgT8AhXHit/waEfolM1s4THtiLY3ETUGSMXvFU= Message-ID: Date: Wed, 21 Jun 2023 20:51:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.1 Subject: Re: [PATCH v2] drm/i915: Replace kmap() with kmap_local_page() Content-Language: en-US To: Ira Weiny , Sumitra Sharma Cc: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Daniel Vetter , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Fabio , Deepak R Varma References: <20230620180759.GA419158@sumitra.com> <79e1f37f-3ffa-0195-860b-08cc890d810e@shipmail.org> <649326df1b895_1c0dd29486@iweiny-mobl.notmuch> From: =?UTF-8?Q?Thomas_Hellstr=c3=b6m_=28Intel=29?= In-Reply-To: <649326df1b895_1c0dd29486@iweiny-mobl.notmuch> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/21/23 18:35, Ira Weiny wrote: > Thomas Hellström (Intel) wrote: >> I think one thing worth mentioning in the context of this patch is that >> IIRC kmap_local_page() will block offlining of the mapping CPU until >> kunmap_local(), so while I haven't seen any guidelines around the usage >> of this api for long-held mappings, I figure it's wise to keep the >> mapping duration short, or at least avoid sleeping with a >> kmap_local_page() map active. >> >> I figured, while page compression is probably to be considered "slow" >> it's probably not slow enough to motivate kmap() instead of >> kmap_local_page(), but if anyone feels differently, perhaps it should be >> considered. > What you say is all true. But remember the mappings are only actually > created on a HIGHMEM system. HIGHMEM systems are increasingly rare. Also > they must suffer such performance issues because there is just no other > way around supporting them. > > Also Sumitra, and our kmap conversion project in general, is focusing on > not using kmap* if at all possible. Thus the reason V1 tried to use > page_address(). > > Could we guarantee the i915 driver is excluded from all HIGHMEM systems? The i915 maintainers might want to chime in here, but I would say no, we can't, although we don't care much about optimizing for them. Same for the new xe driver. Thanks, /Thomas > >> With that said, my Reviewed-by: still stands. > Thanks! > Ira