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=-5.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 5CE76C433E0 for ; Tue, 2 Feb 2021 15:26:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 285D364F5E for ; Tue, 2 Feb 2021 15:26:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235452AbhBBP0T (ORCPT ); Tue, 2 Feb 2021 10:26:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39244 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235404AbhBBPYg (ORCPT ); Tue, 2 Feb 2021 10:24:36 -0500 Received: from mail-wm1-x32d.google.com (mail-wm1-x32d.google.com [IPv6:2a00:1450:4864:20::32d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EEE16C0613D6 for ; Tue, 2 Feb 2021 07:23:55 -0800 (PST) Received: by mail-wm1-x32d.google.com with SMTP id o10so2142948wmc.1 for ; Tue, 02 Feb 2021 07:23:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-disposition:in-reply-to; bh=PBOv4oa0xyBSu7Av2IkfR/vnH44GMIHIBZqxC79Sm/Y=; b=DS825I+YcxBaWeWEl+ZNWlwgUUIR8iQmQPkY4QFjW+uga7eCjkKj/KLKeVvYlbT342 XZW5+2Ar3ZP7nqC+R9oJZP8ayAuB43dHLEmwnU4GvZ9vZ1Wr26KIXGNKp38uQSy6K9Tt lMA+CYFhvJPF2cC1gm5jEgIe+iEoWYF68Djqs= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :in-reply-to; bh=PBOv4oa0xyBSu7Av2IkfR/vnH44GMIHIBZqxC79Sm/Y=; b=JqJHEMUus8vMrskxC9uvuo+G3NT2o3Why8dwrE0qv3Amn4IsW7v0kuzKSvXZhBoa6I KfLet5tHBmGC6mxFuopABZsiU/K/fjCHITszwpaxoPp3zK/IqFvLzcVHEPX1+nmBcaAo FdUvykQzTTaMpsAP9bS0qss0zwrIPNRei81FvYaFNN8HI/mJQT/rBrw1QB0uqY7hyInt mgJ6AipjRFBi60jfxz16c9+A5GURDqF9gyKFORUZo7GlRBiYdPiLzyy4zfJtIVz+7J2P HWEmCaZiadhs8kbxXhUgJm+CxB4oY7BMAizlzxCVzQEN0nWpKAgyHsDko7AL9P6nNvAF b3uA== X-Gm-Message-State: AOAM5313W3aPAGSfdwqzv3wd4dA5zimo+8si8WBeu2Av9Kv9x5pgl40V 4sZI9a+7qGT+USwwzjBb576zSg== X-Google-Smtp-Source: ABdhPJwc4Iu2brOpfruPVn+eCfb6X4r3qeK2Ze160BwejVhNYW1tKRv6W4xHtSFBHQEAxujvrMfubQ== X-Received: by 2002:a1c:f417:: with SMTP id z23mr4176491wma.29.1612279433428; Tue, 02 Feb 2021 07:23:53 -0800 (PST) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id f6sm3373520wmq.33.2021.02.02.07.23.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Feb 2021 07:23:52 -0800 (PST) Date: Tue, 2 Feb 2021 16:23:50 +0100 From: Daniel Vetter To: Phillip Susi Cc: Daniel Vetter , Geert Uytterhoeven , Linus Torvalds , Pavel Machek , Randy Dunlap , LKML , "linux-doc@vger.kernel.org" , Greg Kroah-Hartman , dri-devel , Linux Fbdev development list Subject: Re: fbcon: remove soft scrollback code (missing Doc. patch) Message-ID: Mail-Followup-To: Phillip Susi , Geert Uytterhoeven , Linus Torvalds , Pavel Machek , Randy Dunlap , LKML , "linux-doc@vger.kernel.org" , Greg Kroah-Hartman , dri-devel , Linux Fbdev development list References: <20200916205434.GA10389@duo.ucw.cz> <87czyf5jjp.fsf@vps.thesusis.net> <87k0s4ai33.fsf@vps.thesusis.net> <87wnvqts9g.fsf@vps.thesusis.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87wnvqts9g.fsf@vps.thesusis.net> X-Operating-System: Linux phenom 5.7.0-1-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 02, 2021 at 10:13:14AM -0500, Phillip Susi wrote: > > Daniel Vetter writes: > > > Just a quick comment on this: Since most framebuffers are write-combining, > > and reads from that tend to be ~3 orders of magnitude slower than writes > > (at least on the pile of machines I looked at here, there's big > > differences, and some special streaming cpu instructions to make the > > reading side not so slow). > > > > So scrolling by copying tends to be significantly slower than just > > redrawing everything. > > I know this was the case years ago with AGP as iirc, it doubled ( 4x, 8x > ) the PCI clock rate but only for writes wasn't it? I thought this was > no longer an issue with PCIe, but if it is, then I guess I'll go ahead > with cleaning up the dead code and having it re-render with the larger > text buffer. Still the same with PCIe, probably gotten worse since uncached reads are still as slow, but write-combined writes have gotten much faster even. There's work going on to have a coherent link to gpus which would allow fully cached reads and writes, early with nvlink and now as a standard with CXL (https://en.wikipedia.org/wiki/Compute_Express_Link) But that's aimed at big compute jobs for servers, not really for display. Also some on-die gpus have become fully coherent, but again only for render/compute buffers, not for the display framebuffer. So all together 0 signs this is changing going forward, reading from framebuffers is slow. Ok there's some exceptions: For manual update buffers (defio for fbdev drivers, drm also supports this with an entire set of helpers) the framebuffer used by the cpu is sometimes (but very often still not) cached. Imo not worth optimizing for, since for the drivers where it is cached they either have no blitter, or it's really tiny panels behind spi links and similar, so not going to be fast anyway. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch 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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 844ACC433E0 for ; Tue, 2 Feb 2021 15:23:56 +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 E814464F5C for ; 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Tue, 02 Feb 2021 07:23:53 -0800 (PST) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id f6sm3373520wmq.33.2021.02.02.07.23.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Feb 2021 07:23:52 -0800 (PST) Date: Tue, 2 Feb 2021 16:23:50 +0100 From: Daniel Vetter To: Phillip Susi Subject: Re: fbcon: remove soft scrollback code (missing Doc. patch) Message-ID: Mail-Followup-To: Phillip Susi , Geert Uytterhoeven , Linus Torvalds , Pavel Machek , Randy Dunlap , LKML , "linux-doc@vger.kernel.org" , Greg Kroah-Hartman , dri-devel , Linux Fbdev development list References: <20200916205434.GA10389@duo.ucw.cz> <87czyf5jjp.fsf@vps.thesusis.net> <87k0s4ai33.fsf@vps.thesusis.net> <87wnvqts9g.fsf@vps.thesusis.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87wnvqts9g.fsf@vps.thesusis.net> X-Operating-System: Linux phenom 5.7.0-1-amd64 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linux Fbdev development list , "linux-doc@vger.kernel.org" , Greg Kroah-Hartman , Randy Dunlap , LKML , dri-devel , Geert Uytterhoeven , Pavel Machek , Linus Torvalds Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Tue, Feb 02, 2021 at 10:13:14AM -0500, Phillip Susi wrote: > > Daniel Vetter writes: > > > Just a quick comment on this: Since most framebuffers are write-combining, > > and reads from that tend to be ~3 orders of magnitude slower than writes > > (at least on the pile of machines I looked at here, there's big > > differences, and some special streaming cpu instructions to make the > > reading side not so slow). > > > > So scrolling by copying tends to be significantly slower than just > > redrawing everything. > > I know this was the case years ago with AGP as iirc, it doubled ( 4x, 8x > ) the PCI clock rate but only for writes wasn't it? I thought this was > no longer an issue with PCIe, but if it is, then I guess I'll go ahead > with cleaning up the dead code and having it re-render with the larger > text buffer. Still the same with PCIe, probably gotten worse since uncached reads are still as slow, but write-combined writes have gotten much faster even. There's work going on to have a coherent link to gpus which would allow fully cached reads and writes, early with nvlink and now as a standard with CXL (https://en.wikipedia.org/wiki/Compute_Express_Link) But that's aimed at big compute jobs for servers, not really for display. Also some on-die gpus have become fully coherent, but again only for render/compute buffers, not for the display framebuffer. So all together 0 signs this is changing going forward, reading from framebuffers is slow. Ok there's some exceptions: For manual update buffers (defio for fbdev drivers, drm also supports this with an entire set of helpers) the framebuffer used by the cpu is sometimes (but very often still not) cached. Imo not worth optimizing for, since for the drivers where it is cached they either have no blitter, or it's really tiny panels behind spi links and similar, so not going to be fast anyway. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel